In-form playmaker De Bruyne and right-back Kyle Walker are doubtful for the Wembley game after both missed training on Friday.
Both De Bruyne and Walker hobbled out of City's 0-0 draw at Atletico Madrid in the UEFA Champions League on Thursday (AEST). Walker has a twisted ankle.
Guardiola said De Bruyne's injury was not a muscular issue and mentioned the midfielder's calf and foot when asked about the problem.
To lose him or Walker – or even both senior men – for such a major occasion would be a blow to City.
"We will see tomorrow. Apparently, it will be so close after what happened on Wednesday, but we will see," Guardiola said.
City is chasing a treble of Premier League, FA Cup and UEFA Champions League titles that has only been achieved once before, by Manchester United 23 years ago.
Walker's injury was described by Guardiola as "a big twist, but it's getting better".
"We will see in the next hours, the next days. In football these kinds of things happen. We will adapt, adjust and go from here," Guardiola said. "Kevin had stitches after he had contact – it's not a muscular injury."
City, which has been preparing for the Liverpool game at Millwall's training ground in south London, is feeling the strain at this stage of the season.
It has travelled from Madrid to London, rather than preparing in Manchester and then making another long journey, with Guardiola pointing to the demands of broadcasters as the reason his team must play such an important game less than 72 hours since its previous huge assignment in Spain.
"We have to adapt," Guardiola added.
He said City could "dream to be in better conditions, but it's not going to happen", given the tight turnaround.
De Bruyne scored in last Monday's (AEST) 2-2 Premier League draw with Liverpool, which was also in UEFA Champions League action on Thursday (AEST), reaching the semi-finals at Benfica's expense.
"We're going to perform well. Like I said to the players, I don't want any excuse," Guardiola said.
"It is what it is and for that we have to go there tomorrow in Wembley Stadium and try to do our game."