Lionel Messi returned to training on Monday after recovering from a stomach bug that caused him to miss Barcelona's goalless draw against Malaga on Saturday.
Red Star Belgrade, who won Europe's premier club competition in 1991, engineered a 2-0 home victory against HJK Helsinki thanks to a Richmond Boakye header and substitute Milan Pavkov's sweeping 90th-minute finish.
Manager Pep Guardiola tempered his delight at ManchesterCity's ability to fight back three times in a thrilling 3-3 draw against Celtic in the Champions League on Wednesday by urging his players to understand the importance of a good start.
Celtic manager Brendan Rodgers has a goalkeeping dilemma to resolve before ManchesterCity turn up for their Group C Champions League match in Glasgow on Wednesday.