De Bruyne was replaced in the 86th minute of City's 2-0 EFL Cup fourth round win over Fulham after colliding with Timothy Fosu-Mensah and limped off the pitch clutching at his left knee.
The Belgian has only recently recovered from cruciate ligament damage to his right knee and was assessed by City’s medical staff after the final whistle.
“He’s being checked by the doctors,” Guardiola said in his post-match press conference. Asked whether he was worried about De Bruyne’s injury, the City manager said: “I don’t know right now. I don’t know.”
The win over Fulham, sealed by two goals from youngster Brahim Diaz, was De Bruyne’s second start since returning from a two-month knee injury lay-off after playing against Shakhtar Donetsk last week.
De Bruyne appeared as a second-half substitute in the victory over Tottenham Hotspur at Wembley on Monday night and appeared to be approaching full fitness against Fulham.
“I think today Kevin is back, no? It’s the Kevin we know,” Guardiola said of his performance. “He made a huge effort in Donetsk against Shakhtar. He played a few minutes in a difficult situation against Spurs.
“It was a difficult situation because of the pitch and the conditions and tough physicality but today again he was involved in the offensive and defensive side, in the pace, in the set pieces, the passes and assists.
On the injury, Guardiola added: “Hopefully what happened in the last minutes is not serious.”
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