Sergio Aguero missed two days of training after Manchester City's Premier League draw with West Brom due to a new injury problem.
Aguero played 14 minutes in the West Brom game, his first league appearance since October, as Pep Guardiola tries to manage the return of his star striker.
Guardiola has been careful not to rush Aguero back, having twice seen him suffer setbacks after coming back from his knee surgery in the summer.
Now, Guardiola has confirmed Aguero suffered a new reaction after his cameo against West Brom, although he was able to return to training on Friday to put him in contention for another appearance at Southampton.
Guardiola said: "I don't know. After the game he could not train, yesterday no training, today he trained.
"He trained really well but I don't know how many minutes [he will play against Southampton].
"It's important he can make training sessions. Unfortunately after the game he could not, nothing about the knee. Unfortunately a different position. Today he trained."
Guardiola also confirmed that Kevin De Bruyne will play at Southampton after dismissing a question that the playmaker could be rested over the Christmas period.
The manager said: "No, he is so important for us that he won't rest. He rested in the Champions League previously and right now we need him."
