Manuel Pellegrini fears Kevin De Bruyne suffered damage to his medial knee ligament in Manchester City's League Cup semi-final win over Everton on Wednesday.
The Belgium international came off the bench to inspire City to a 3-1 second-leg win and 4-3 aggregate triumph with a goal and an assist for Sergio Aguero.
De Bruyne had to be carried off on a stretcher during injury time, however, having had his right leg strapped in a brace after he went to ground in clear discomfort, and Pellegrini says club doctors are concerned.
"The doctors think it could be his medial ligament but we will know more tomorrow," he told Sky Sports after the match.
Pellegrini was nonetheless delighted with his side's display as City came from behind to record the victory, and claims Aguero - who has now scored five goals in his last three matches - is approaching a return to top form.
"I think so because he scored in the last two games. Tonight he scored, he had a shot on the post, he's always creating a lot of danger so I think he's back to his best," he said.
City now face Liverpool in the final at Wembley on February 28 and Pellegrini believes lifting the trophy could set his players up for significant success during the remainder of the season.
"We have one month to think about the final. We need time to prepare for that game," he added.
"It will be a very close, very tough game, but we're optimistic we can play a good game. I think it's important to win a title in February, especially when you're involved in other competitions."