The South Korean outfit were crowned champions of Asia just last month when they defeated Persepolis of Iran 2-1 in the final.
While the new campaign will only kick off in April, the draw for the group stage was conducted on Wednesday and Ulsan were drawn in Group F alongside first-timers BG Pathum United of Thailand and Vietnam's Viettel FC and a yet-to-be-determined playoff winner, which could Beijing Guoan - the team they defeated in last year's quarter-finals.
Malaysia's Johor Darul Ta'zim, who have emerged as a rising force in recent years, are likely to be quietly confident in their prospects of reaching the knockout round.
Chinese Super League champions Jiangsu should emerge as their toughest test in Group G, but JDT's performances in the past two years suggest they could potentially match it with Nagoya Grampus of Japan and the winner of playoff between Pohang Steelers (Korea Republic) and Ratchaburi Mitr Phol (Thailand).
The expansion of the ACL to 40 teams this year means several nations will be represented for the first time in years, and Singapore's Tampines Rovers have not been dealt a favourable hand as they will come up against Jeonbuk Hyundai Motors (Korea Republic), Gamba Osaka (Japan) and Sydney FC.
The West Zone also threw up some tantalising match-ups but it is difficult to look past Group C, which will see Qatari champions Al Duhail take on Al Ahli (Saudi Arabia), Esteghlal (Iran) and Al Shorta (Iraq) - with all four teams having been regular features in Asia's premier club competition in recent times.
AFC CHAMPIONS LEAGUE 2021 DRAW
Group A: Al Hilal (Saudi Arabia), Shabab Al Ahli (United Arab Emirates), Istiklol (Tajikistan), West Zone playoff 1 winner
Group B: Sharjah (United Arab Emirates), Tractor (Iran), Pakhtakor (Uzbekistan), West Zone playoff 2 winner
Group C: Al Duhail (Qatar), Al Ahli (Saudi Arabia), Esteghlal (Iran), Al Shorta (Iraq)
Group D: Al Sadd (Qatar), Al Nassr (Saudi Arabia), Al Wehdat (Jordan), West Zone playoff 3 winner
Group E: Persepolis (Iran), Al Rayyan (Qatar), Goa (India), West Zone playoff 4 winner
Group F: BG Pathum United (Thailand), Ulsan Hyundai (Korea Republic), Viettel (Vietnam), East Zone playoff 1 winner
Group G: Jiangsu (China PR), Nagoya Grampus (Japan), Johor Darul Ta'zim (Malaysia), East Zone playoff 3 winner
Group H: Jeonbuk Hyundai Motors (Korea Republic), Gamba Osaka (Japan), Tampines Rovers (Singapore), Sydney FC (Australia)
Group I: Kawasaki Frontale (Japan), Guangzhou (China PR), United City (Philippines), East Zone playoff 4 winner
Group J: Shandong Luneng (China PR), Port (Thailand), Kitchee (Hong Kong), East Zone playoff 2 winner