Manchester City striker Sergio Aguero could miss his team's next two games after injuring his hamstring in the 3-0 victory over Stoke City on Tuesday.
The Argentine, City's top scorer last term, was forced off the Etihad Stadium pitch moments after converting a 74th minute penalty against the Potters.
Aguero has been ruled out of Saturday's FA Cup clash with Watford, while he is doubtful for a January 13 trip to Arsenal.
Citizens first-team coach David Platt said: "It is difficult to assess an injury like that, how long it is going to be.
"He'll certainly be out Saturday and in my experience he'd be doubtful for Arsenal.
"But there are different degrees of hamstring injuries - that's why we need 48 hours.
"It is not just, 'It's a hamstring and this is how long it will be' - we have just got to wait.
"There will be a lot of swelling and a bit of bleeding in there. We don't know how it is going to settle down.
"It's a blow but unfortunately, when you have got so many games in a short space of time, you are running the risk with everybody."