Sergio Aguero will remain under observation for the next three months after he was diagnosed with a heart problem.
The Barcelona star was rushed to hospital for tests after he complained of breathing difficulties during his side's 1-1 draw with Alaves.
The 33-year-old was diagnosed with having cardiac arrhythmia - an irregular heartbeat.
A Barcelona statement on Monday read: "Aguero has been subjected to a diagnostic and therapeutic process by Dr Brugada.
"He is unavailable for selection and, during the next three months, the effectiveness of treatment will be evaluated in order to determine his recovery process."
Aguero later announced: "I am well and in good spirits to face the recovery process. I want to thank you all for so many messages of support and love that make my heart stronger today."
Aguero began experiencing problems following a coming together with Alaves centre-back Victor Laguardia on Saturday.
Sergio Aguero will remain under observation for the next three months ( Image:
REUTERS)
The former Manchester City star was able to get back to his feet but was in clear discomfort and was replaced by Philippe Coutinho just before half time.
Aguero's heart rate was said to be much higher than it should have been and he was taken to hospital via ambulance.
He will remain in the hospital for the next few days but will not be able to play football again for at least three months.
Sergi Barjuan is serving as Barcelona's interim manager following the sacking of Ronald Koeman and recalled the moment in his post-match interview.
"I asked him and he told me he was dizzy," said Barjuan of Aguero. "I was told he went to the hospital. I don't know anything else."
Aguero was making just his fifth appearance for Barcelona having missed the start of the season with a calf injury.
Aguero's former Man City teammate Raheem Sterling tweeted shortly after the Argentine was taken to the hospital, writing: "Stay strong my brother @aguerosergiokun, we're all with you. Get well soon."
Manchester City's official Twitter account also sent their best wishes to Aguero, tweeting: "Everyone at Manchester City wishes you a speedy recovery, @aguerosergiokun. We're with you."