The Portugal international missed all five matches in November with a calf problem but returned at the start of December and has been an ever-present this month.

But he will not be available for City's trip to Aston Villa on Saturday, while there is uncertainty about the fitness of goalkeeper Ederson.

"Ruben is out for a long time and Ederson, I don't know if he will be ready tomorrow," Guardiola said on Friday.

The City boss added that Dias would be out for "three or four weeks".

"After 75 minutes against United he felt something," he said. "He's strong and wanted to stay on the pitch but now he's injured."

Injury-hit City have suffered a dramatic collapse in form over recent weeks, losing eight of their past 11 games in all competitions and are fifth in the Premier League table.

Nathan Ake remains out but fellow defenders Manuel Akanji and John Stones are back in full training.

"Manuel and John are back in training," said Guardiola. "That is good for us. As many players that are back the better.

"I don't know yet (if they can start against Aston Villa). Yesterday was their first training session, I would say, properly. They have been out for a while."

City's current run is the worst of Guardiola's managerial career, which has included glittering stints at Barcelona and Bayern Munich.

But he was defiant ahead of the trip to Unai Emery's Villa, who are in seventh place in the table.

"If you fall down six times, you have to stand up seven," he said. "There's not an alternative.

"I am fine. I am a normal person. When it is going well I am better, when it is not going well professionally we are more concerned about what we have to do.

"We have to start again but we don't know what will happen (at Villa Park). We have to try it again and sooner or later it will turn around."