De Bruyne was not included in the matchday squad for the UEFA Champions League draw with RB Leipzig last Wednesday due to illness.
The Belgian was back on the bench at Bournemouth at the weekend but was not called upon during the 4-1 win.
While De Bruyne is still not 100% fit, Guardiola has stated he is improving.
“Still a little illness but he is better,” the boss said when asked about the midfielder.
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Laporte was also not involved in last week’s matches while Stones has not featured since the FA Cup fourth round win over Arsenal at the end of January.
While the central defenders are believed to be nearing a return, Guardiola cannot yet be sure if they will face the Robins at Ashton Gate.
“We are training this afternoon,” he said, when asked about the availability of the pair.
Tuesday will be the first meeting between the two Clubs in the FA Cup, although we did face off in the 2017/18 League Cup semi-final with City winning 5-3 on aggregate.
Guardiola expects a tough test against the side ranked 13th in the Championship.
“Last 12 games, no defeats. This means they are there,” he said.
“My scouts said they are a good team, a manager with experience and did well at Leicester City. It’s a final, FA Cup is an important competition. A serious team will play tomorrow.
“My experience in this country, when you go away in FA Cup against a Championship team is always tough. At home it would be different but away is always tough.”
Bristol City v City
City travel to Bristol City for a 20:00 (UK) kick-off and you can follow the game across mancity.com and our official app.
We will start live updates at 18:00 on our Matchday Centre and that will run throughout the evening.
Our Matchday Live programme will begin shortly before team news arrives at 16:30. Natalie Pike will be in the studio with Nedum Onuoha, Esme Morgan, Shaun Goater to give you a City-centric view on events at Ashton Gate.
During the game, Alistair Mann and Michael Brown will talk you through proceedings with our radio commentary offering.
Afterwards, we will bring you all the reaction before highlights are available from midday on Wednesday.
CITY+ subscribers can watch the entire 90 minutes back from midday on Wednesday too.
