Pep Guardiola says it is too early to judge the extent of Vincent Kompany's injury at this stage.
The City skipper walked off the pitch in the last few moments of the 2-1 win over Swansea with what must be assumed to be an injury of some sort.
Guardiola is waiting for the assessment of his medical team which is likely to be known in the next few days.
"The doctors are speaking with him and seeing what's up," said the Blues' boss.
"Hopefully it will not be a big problem, We're going to wait for the results from the doctors and I still don't have that or the opinion of my staff.
Kompany was making his first appearance since the Champions League semi-final against Real Madrid and had an impressive return at The Liberty Stadium.
Any set-back would be a huge blow to the player and the Club - though there is no indication either way at present.
The boss praised the Belgian's performance saying: “It was good. It's not easy after a long, long time without playing, defensively he was so strong and he played really good.”
"After they scored the goal, I asked: 'What happened?' They said that Vincent had gone to the locker room,but hopefully it will not be a big problem. We will have to wait.
“If he's injured, he's injured, he cannot stay on the pitch. As I say, I don't know what happened. The doctor is testing, looking at what's going on and after we'll see.”