Manchester City fear they will be without Martin Petrov for a "significant time" after revealing the winger has suffered knee ligament damage.
Petrov was substituted at half-time of Bulgaria's midweek World Cup qualifier against Georgia and initial scans have revealed some degree of ligament damage.
The 29-year-old wideman has been restricted to just two substitute appearances in recent weeks due to hamstring and knee problems prior to heading off on international duty.
"He has ligament damage, we're hopeful that the news will be positive but at this time the initial scans don't look very good so there is a real concern that he could be out for a significant time," manager Mark Hughes told the club's official website.
"He had only had ten minutes in one game and 20 minutes in another prior to then playing 90 minutes for his country.
"It's a big ask for these players and they are at risk if they have not had the required amount of time before going away to an international. Our problem is that we have to allow them to go."
Meanwhile, Hughes believes Robinho will be fit to face Newcastle United on Monday evening despite being stretchered off while playing for Brazil against Colombia on Wednesday.
The British record signing was initially thought to be a major doubt for the trip to Tyneside.
"We are still waiting for definite news on it, but we are taking the view that we have heard nothing from Brazil's medical department, so we will make the assumption that he is fit and well," continued Hughes.
"I have had a look at the tape of the incident where he got the injury and looking at the pictures it does not look like a significant injury.
"It was just a clash so we will expect him to be fit and well when he returns."