One of the biggest and most successful sides in Asian football, Al Hilal have no fewer than seven continental titles to their name. After winning the 2019 AFC Champions League they were forced to withdraw from the 2020 edition due to COVID-19, but having beaten Esteghlal FC in the last 16 they are back in the latter stages and looking to make it two titles in three years.

A number of stars remain from that victorious 2019 campaign, including top scorer and MVP Bafetimbi Gomis, Salem Al Dawsari and Salman Al Faraj. Further quality has been added with the likes of Brazilian Matheus Pereira and Saleh Al Shehri, who has shone for Saudi Arabia in the AFC Asian Qualifiers – Road to Qatar.

Under former Monaco boss Leonardo Jardim, Al Hilal remain unbeaten six games into the 2021-22 Saudi Pro League season, but they have yet to really click into gear. 

After opening the season with back-to-back wins, the Riyadh giants have drawn three of their past four domestic games heading into the quarter-finals.

Few clubs have performed as consistently over recent years as Persepolis, who have appeared in two of the past three finals as well as reaching the semi-finals in 2017. However, that first AFC Champions League title continues to elude them as defeats to Kashima Antlers in 2018 and Ulsan Hyundai in 2020 saw them fall just short at the last.

The Tehran giants' success has led to a number of stars departing, with Bashar Resan, Shojae Khalilzadeh and Ahmad Noorollahi, among others, all heading to pastures new over the past year. However, Yahya Golmohammadi's side still boast star power in the likes of Mahdi Torabi and Vahid Amiri, while the ever-dependable veteran Seyed Jalal Hosseini is an inspirational presence both on and off the pitch.

Persepolis lifted their fifth successive Iranian Pro League title in July as their dominance in the Islamic Republic of Iran continued. 

The current campaign does not get underway until after the AFC Champions League quarter-finals, meaning their last game was the 1-0 victory over FC Istiklol in the Round of 16, when Torabi struck a last-minute winner.

Historically Al Nassr have not performed as well in the AFC Champions League as some of their Saudi counterparts, but they have improved in recent years and are in the quarter-finals for the third successive campaign. Last year's semi-final showing marked their best run to date, although they previously achieved continental glory by winning the 1997-98 Asian Cup Winners' Cup.

For a number of years, Abderrazak Hamdallah has been Al Nassr's standout player, and the Moroccan striker's seven goals saw him scoop the Top Scorer award in 2020. Elsewhere, the arrival of Brazilian Anderson Talisca adds genuine quality going forward, while Vincent Aboubakar marked his AFC Champions League debut with the only goal in the Round of 16 win over Tractor FC.

At the early stages of the 2021-22 Saudi Pro League season, Al Nassr sit third in the standings and with a game in hand on the top two. 

They have won four of their six games to date, including their last two heading into the quarter-final meeting with Al Wahda, as they aim to pick up their first title since 2018-19.

Abu Dhabi side Al Wahda are back in the quarter-finals for the first time since 2007 when they made the semi-finals for the only time in their history. The four-time UAE Pro League champions' last appearance in the knockout rounds, meanwhile, came in 2019 when they were eliminated by Saturday's opponents Al Nassr.

The big news ahead of the 2021 campaign was the arrival of 2017 AFC Player of the Year Omar Khribin, and both he Brazilian João Pedro have been in good form in recent weeks. The evergreen Ismail Matar, who was part of the run to the 2007 semi-finals, is still going strong at the age of 38 having spent more than two decades with the club.

After scraping past United Arab Emirates rivals Sharjah on penalties in the Round of 16, Al Wahda's domestic form has followed a similar path: they are hard to beat but struggle to win. 

Six games into the UAE Pro League season, they are undefeated but have drawn their last five league games in a row.

The defending champions won a record-equaling nine games in a row to lift the 2020 title with the 2-1 victory over Persepolis in the final matching the run they produced en route to being crowned kings of Asia in 2012. Six successive group stage wins this year took their winning streak to 15 and, after seeing off Kawasaki Frontale on penalties in the last 16, they are now unbeaten in 17 on the continent.

Ulsan boast a squad with excellent strength in depth. The likes of Lee Dong-jun, Lee Dong-gyeong and Won Du-jae are among the hottest prospects in Korea Republic, Lee Chung-yong and Yoon Bit-garam offer valuable experience and quality, while Georgian international Valeri Qazaishvili has dazzled on occasions this year.

Domestically they find themselves in a familiar position at this stage of the K League 1 season, ahead of Jeonbuk Hyundai Motors. 

They have won their past three games heading into the quarter-final with the Jeonju side, who they sit a point above but have been pipped at the post by in the past two seasons.

Two-time AFC Champions League winners Jeonbuk are back in the quarter-finals for the first time since 2018. Since last being crowned kings of Asia in 2016, they have won four successive K League 1 titles but have failed to hit the heights expected of them on the continent.

However, the Jeonju side are looking like real contenders in the current campaign, with goals raining in from the likes of Gustavo and Stanislav Iljutcenko. Song Min-kyu boasts bags of potential and Paik Seung-ho is showing his true quality now back in his homeland, while full-backs Lee Yong and Kim Jin-su offer a considerable threat going forward.

Like Sunday's opponents Ulsan, Jeonbuk are on an excellent run of form of late as they aim for a fifth K League 1 title on the bounce.

Since edging past Thailand's BG Pathum United on penalties in the last 16, Kim Sang-sik's side have won four consecutive games domestically.

Making just their fourth appearance in the AFC Champions League, Nagoya Grampus have never failed to make the knockout rounds. Although the Round of 16 victory over Korea's Daegu FC ensured they advanced into the last eight for only the second time having also reached the semi-finals in 2009.

The J1 League side breezed through the group stage unbeaten with the likes of goalkeeper Mitch Langerak, Mateus and Yoichiro Kakitani all starring. It was new arrival Jakub Swierczok who took centre stage in the last 16, meanwhile, the Polish striker netting a hat-trick in the 4-2 win.

Domestically, Massimo Ficcadenti's side are someway off the pace set by Kawasaki Frontale but are well in the hunt for a top-three finish.

Form over their past five games has been somewhat inconsistent, although last weekend they secured their place in the J.League Cup final after overcoming FC Tokyo.

AFC Champions League winners in 2009, Pohang Steelers are a three-time continental champion having also lifted back-to-back Asian Club Championships in the 90s. But in recent years they have only fleetingly appeared in the competition, and this year's run marks the first time they have reached the quarter-finals since 2014.

Under Kim Gi-dong, who was part of the 2009 title-winning squad, Pohang reached the Round of 16 as one of the best-placed runners-up before claiming an impressive victory against Cerezo Osaka in Japan after Lee Seung-mo's decisive goal. Lim Sang-hyub should offer another goal threat against Nagoya, while Shin Jin-ho is targeting back-to-back AFC Champions League titles after captaining Ulsan to glory last year.

Pohang's K League 1 form has been poor of late as they suffered three successive losses on the back of defeating Cerezo and dropped into mid-table. However, a 3-2 win over Gwangju in their last outing may just have restored confidence ahead of the quarter-finals.

*Poll ends at 22:00 (UTC+8) on October 16