Manchester City striker Sergio Aguero says "everything went well" after having surgery on his injured knee.
The Argentine had travelled to Barcelona to see a knee specialist amid fears his season might be over.
His manager Pep Guardiola said it is too early to put a timescale on the 32-year-old's return to action.
Asked if Aguero would be fit for the resumption of the Champions League on 7-8 August, City's Spanish boss said: "I don't know right now."
He added: "Once he has finished the surgery we will know the time Sergio will come back to play with us."
Aguero was forced off before half-time in the home side's 5-0 Premier League win over Burnley on Monday, following a challenge by defender Ben Mee.
However, in his post-match interviews, Guardiola revealed Aguero had a knee problem before the match.
City are due to face Real Madrid in the second leg of their Champions League last-16 tie with a 2-1 lead from the first leg in Spain.
On Wednesday the player tweeted: "Everything went well and I will soon start with the recovery.
"Thank you so much to Dr. Cugat and his team and everyone for so much support."