Man City's Johnson undergoes surgery
The England Under-21 international was forced out of City's 1-0 win over Sunderland at half-time following a recurrence of the groin injury which has plagued him for most of the season.
"Michael cannot go on like this," confirmed the Swede.
"He is only a young man but he cannot train the day after a match.
"He came to me at half-time and said he couldn't run anymore.
"We must decide whether to send him for an operation and, with the international break, now would be a good time.
"I am not sure how long he will be out but I don't think it will be any more than two or three weeks."