Manchester City boss Manuel Pellegrini says he is delighted with his side's performance against Sunderland but also that Vincent Kompany's calf injury is a concern.
The defender was making his long-awaited comeback from injury but was forced out of the game a few minutes after coming on as a substitute.
His injury overshadowed the Citizens' win who consolidated their position in the top three.
"I don't think the score reflected the difference between the two teams," Pellegrini is quoted as saying by the BBC.
"I am happy that the performance was very good, we played attacking football, and I am happy with the individual performances. The only pity was Vincent Kompany's injury.
"It is a calf. Nobody understands.
"He had a good warm up, he was working during the week with normality. It is difficult to understand. The most important thing is to understand why this happens. That is the most important to focus on now.
"The team performance was the most important. I saw we were returning to our normal performance as a team. It is important to continue. We have just finished the first round of fixtures.
"Next we have to play against Leicester. Nobody wins the title in December, but it doesn't mean it will be easy to beat Leicester. In the second half of the season we have to play teams around us. It is important to try to continue with this kind of performance."