Sergio Aguero's knee injury suffered against Burnley "doesn't look good" according to Manchester City manager Pep Guardiola.
Aguero was substituted just before half time after feeling pain in his knee during Manchester City's 5-0 win over Burnley.
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The Argentine forward lasted just short of 45 minutes on his first start since the Premier League restarted.
Aguero played the final 10 minutes of the match against Arsenal last Wednesday after struggling with the problem during training before the season restarted.
Guardiola said: "It doesn't look good, something in the knee, we will see tomorrow (Tuesday) in a better way what he has. He was struggling in the last month about pain in his knee, we will see.
Asked whether he was worried Aguero would miss the rest of the season, Guardiola answered: "Tomorrow we will see.
"I am not a doctor, but it doesn't look good."
Manchester City are still competing on two fronts away from the Premier League. They will be hoping to add the FA Cup and the Champions League to the League Cup they won in March.
The games are coming thick and fast for City who go to Stamford Bridge to face Chelsea in the Premier League on Thursday before a trip to Newcastle in the FA Cup quarter-finals on Sunday.
City's Champions League last-16 second leg against Real Madrid will take place on August 7 or 8.