MANCHESTER -- Sergio Aguero faces a race against time to be fit for Manchester City's key game at Arsenal later this month.
Aguero, who has missed City's last three games with an ankle injury, will sit out Saturday's home match against struggling Swansea.
The Argentine is set to return to training next week and manager Manuel Pellegrini is optimistic he will be fit to feature against the Gunners on Dec 21.
"I hope next week he will start working with the squad on Tuesday or Wednesday," Pellegrini said in a news conference.
"We play on [the following] Monday against Arsenal so I hope he will be fit for that game. Aguero is improving, but he will not be ready for this weekend."
City will welcome back defender Martin Demichelis against managerless Swansea after he missed the 4-2 Champions League win over Borussia Monchengladbach on Tuesday.
"Martin Demichelis was just a precaution last game," Pellegrini added. "He had a problem with his tendon. He is in the squad list."
But defenders Vincent Kompany and Pablo Zabaleta, along with midfielders Fernando and Samir Nasri, remain sidelined and neither midfielder will be back before Christmas.
Pellegrini hopes skipper Kompany, who has had a calf problem, and Zabaleta, who has struggled with a knee injury, will also be back in training next week.
"Fernando and Zabaleta are not ready yet," he said. "Fernando has a muscle injury so he will have at least two or three weeks more [out]. I hope next week Pablo and Vincent Kompany can start working. Samir Nasri is long term."
Pellegrini has defended Garry Monk, who was sacked as Swansea manager on Wednesday -- only seven months after taking the Welsh club to their highest Premier League finish.
"I don't think the problem of Swansea was the manager," he said. "He was the same manager who made a very good season last year. Every team plays better if you continue with the same manager."