London - Manchester City manager Manuel Pellegrini insists Sergio Aguero's heel injury is not serious even though he doesn't know when the Argentina striker will return.
Aguero has missed two games since limping out of last month's victory over Southampton and will again be absent when City wrap up their Champions League group stage fixtures against Borussia Monchengladbach at Eastlands on Tuesday.
Both Pellegrini and Aguero have played down the problem, but the 27-year-old also seems unlikely to return before the Premier League visit of Swansea on Saturday.
Asked on Monday if the injury was proving more serious than thought, Pellegrini told reporters: "No, but it is an injury that he cannot work (on). He needs time to recover from that problem but it is not a serious injury, it is a pain injury.
"We hope (he will return this week) but we must see the way he improves in the next days. When he can run with normality he can work but if he cannot operate with his heel it is very difficult for him to do."
City, already through to the Champions League last 16, have been hit by a series of injuries to key players this season.
Vincent Kompany missing the last five games with a calf problem, while Aguero also had an earlier spell out with a hamstring issue and David Silva only recently returned after a near two-month absence.
Samir Nasri is a long-term casualty, Fabian Delph missed most of the opening three months of the season and other key players such as Joe Hart, Yaya Toure and Pablo Zabaleta have had time out.
Pellegrini is uncertain when influential captain Kompany might be back in contention.
"Vincent is improving. He is doing some tests on his calf, on which is the best way for him to improve. We will see in the next days when he can return," Pellegrini added.
All the injuries have played a role in City's recent struggles, which continued with a 2-0 loss at Stoke on Saturday, but Pellegrini claims it is too early to assess the performance of back-up players.
"I always say I prefer to play with the whole squad then I can choose the best XI starters, but if the starting XI has six or seven players injured we must make a balance of the whole season. You cannot have a conclusion after one game," he said.
Asked directly if the likes of Wilfried Bony, Nicolas Otamendi, Martin Demichelis or Eliaquim Mangala were not delivering, Pellegrini said: "I analyse the individual performances with the players, not with the press."