Aymeric Laporte is expected to be out of action for three to four weeks due to a hamstring injury.
Laporte got injured in the first leg of the Champions League against Real Madrid.
Now he will miss the Carabao Cup final against Aston Villa on Sunday.
The Frenchman is unlikely to feature in the Manchester derby on March 8 and is also there is a doubt for the return leg against Madrid at the Etihad on March 17.
Guardiola commented on the condition of the player, who just got back from injury and now has one again: "When we are talking about hamstring injury, [the] prognosis is about three weeks to one month, more or less.
"We have tried to avoid the injury but it still has happened. When you have a demanding game to play it happens sometimes."
On the other hand, Leroy Sane might return in the game against U23 Arsenal. The German has not played since suffering anterior cruciate ligament damage just at the beginning of the season and Guardiola will not rush him to come back in the first team quickly.
Guardiola commented on Sane's return: "First we want to see how the game goes, speak with him, and see how he felt against Arsenal. But i think it's good."
City are 22 points behind the leaders in the Premier League table Liverpool and Guardiola believes that if all his players weren't injured the results might be different.
"Well, as you know a manager needs all his players," said Pep. "Yes, of course all of our players are just great, but if you want more variety in the game you need all of them to be fresh, rested and in a good health."
He added: "To be in all of the competitions you need a top talented players and the manager depends absolutely, one hundred per cent on the quality of his team."