The attacker is set to miss the clash with Premier League champions Liverpool due to a fresh hamstring setback after returning from a lengthy lay-off
Pep Guardiola fears Sergio Aguero could be out for as much as a month after the Manchester City striker suffered a hamstring injury.
The Argentine has not travelled to Marseille for his club's second Champions League clash and is expected to miss next month's Premier League match-up with Liverpool.
Guardiola hopes he could be back sooner but the injury is another blow for City, who flew to France on Monday without a recognised striker.
“It depends on the injury, 10-15 days is the minimum,” Guardiola said. “If it’s a little bit longer it will be three weeks, one month.”
Guardiola does at least have Kevin De Bruyne fit again after he came off the bench in Saturday's draw, while Aymeric Laporte has travelled to France after missing City's last three matches.
But they are still without Gabriel Jesus, however, who is stepping up his recovery from the thigh injury he suffered in the opening game against Wolves, while academy forward Liam Delap is not eligible after being left out of the squad submitted to UEFA.
“Kevin is back again, he played a few minutes at West Ham,” Guardiola added. “Aymeric is back, Nathan [Ake] is so close, Gabriel is a week to 10 days to returning. The rest will be two or three weeks - Sergio and [Benjamin] Mendy.”
Jesus is still to return to first-team training, although he hopes to be back on the pitch later this week, while Delap is available for the Premier League and Saturday's trip to Sheffield United.
Guardiola said they considered adding another striker in the last transfer window but decided to strengthen in other areas.
“We thought about it, another type of striker, but we couldn't [do it],” he added.
“It’s not a club that wants revenues at the end of the year, they want what’s best for the team. Our team is young in many positions and we have guys with experience.
“If you decide to buy a striker, it has to be a striker in the league of Gabriel and Sergio. But we cannot afford it.
“I’m not saying the club didn’t want to do it, not just in terms of strikers but in every position, but we thought: Okay, Sergio is back. We didn’t expect Gabriel to be injured but sometimes it happens.”
Defenders Mendy and Ake are also missing from the squad that travelled to France, with injury and illness having ravaged Guardiola's squad in the early weeks of the season.
Guardiola said he must carefully manage his squad but warned that he expects all top clubs to lose players to muscle injuries because of the gruelling schedule that is seeing them play twice a week up until the New Year.
“We are not an exception compared to the other teams in Europe, we’re on the same schedule,” he said. “Now it is recovery and preparation, recovery and preparation, recovery and preparation. We don’t have time to practice much.
“Everyone got the statistics than in the Premier League; we have 47 per cent more muscular injuries than the same period last season. It’s not just about City, it's about everyone.
“Now we have to protect the players as best as possible. The strongest ones will survive, the others will fall down.”