The South Korean giants triumphed in Asia's premier club football tournament for the second time last month after a Junior Negrao double gave them a 2-1 victory over Iran's Persepolis.
In the draw for the group stage, Persepolis, who were also Champions League runners-up in 2018, were placed in the same group as Al Rayyan of Qatar and India's FC Goa.
Meanwhile 2019 champions Al Hilal of Saudi Arabia were drawn against Shabab Al Ahli of the United Arab Emirates and FC Istiklol of Tajikistan.
Two-time champions Jeonbuk Hyundai Motors of South Korea will face Japan's Gamba Osaka and Australia's Sydney FC in Group H.
China's Guangzhou Evergrande, who have also won the title twice, were drawn against Japan's Kawasaki Frontale and United City FC of the Philippines.
This year's tournament has been expanded to 40 teams, from 32 previously, and the group stage matches will take place in one West Asian and one East Asian hub from mid-April.
The two-legged final will take place in November.
The 2020 Champions League was thrown into disarray by the coronavirus pandemic, but was finally completed in a bio-secure "bubble" in Qatar.
Group A: Al Hilal (KSA), Shabab Al Ahli (UAE), FC Istiklol (TJK), play-off winner
Group B: Sharjah (UAE), Tractor FC (IRN), Pakhtakor (UZB), play-off winner
Group C: Al Duhail (QAT), Al Ahli (KSA), Esteghlal (IRN), Al Shorta (IRQ)
Group D: Al Sadd (QAT), Al Nassr (KSA), Al Wehdat (JOR), play-off winner
Group E: Persepolis (IRN), Al Rayyan (QAT), FC Goa (IND), play-off winner
Group F: BG Pathum United (THA), Ulsan Hyundai (KOR), Viettel (VIE), play-off winner
Group G: Jiangsu FC (CHN), Nagoya Grampus (JPN), Johor Darul Ta'zim (MAS), play-off winner
Group H: Jeonbuk Motors (KOR), Gamba Osaka (JPN), Tampines Rovers (SIN), Sydney FC (AUS)
Group I: Kawasaki Frontale (JPN), Guangzhou Evergrande (CHN), United City (PHI), play-off winner
Group J: Shandong Luneng (CHN), Port FC (THA), Kitchee (HKG), play-off winner