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De Bruyne did not feature in Manchester City's 1-0 win on Wednesday, as Sergio Aguero fired the lone goal in the victory over the 12th-place Championship side.
The Belgian star has featured in 35 total matches for the club this season, scoring nine goals with eight of those coming in the Premier League.
However, it appears that De Bruyne could miss time with an injury that could potentially keep him out of action for this weekend's Manchester derby at Old Trafford.
"He [Kevin de Bruyne] fell down in a bad position and had a problem with his back," Guardiola said.
"We don't know how long [he'll be out for with Manchester derby on Sunday], hopefully not that much."
Manchester City currently sit second in the Premier League, 22 points behind league leaders Liverpool with a game in hand.
Guardiola's side is maintaining a seven-point lead over third-place Leicester as well, with the Foxes also having played an extra match.
With Wednesday's victory, Manchester City booked a date with Newcastle in the FA Cup quarter-finals, which will be played on March 4.
"The important thing is that we are there. We want to be in the draw. We are in the draw," Guardiola said.
"This is our fourth game away in a row and we have another one at Old Trafford. We spend a lot of mental energy in the last games. The players were ready.
"We didn't concede one shot on target that means a lot. The second half was better than the first because we found better the spaces where we should move. We are still alive.
He added: "Of course we can be concerned but we can correct a few things. Continue with this pace, don't concede free-kicks and corners.
"We didn't concede once and that means a lot for our capacity to read the game. We scored a goal and we could have scored much more."