Sergio Aguero is facing at least three months out of action after being hospitalised with chest pains.
The Argentine striker has been assessed having been taken off in Saturday's 1-1 La Liga draw with Alaves at the Camp Nou.
Aguero was replaced four-minutes before the break by Philippe Coutinho in what was only his fourth league game since joining on a free transfer from Manchester City in the summer.
The 33-year old was later diagnosed with an irregular heartbeat.
Barcelona confirmed on Monday that Aguero will not play again until at least the spring.
In a statement they wrote: "The first team player Sergio Aguero has been subjected to a diagnostic and therapeutic process by Dr.Josep 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.
"The Argentine was taken to hospital for cardiological evaluation on Saturday following the Barça v Alavés game in which the Barça striker felt unwell in the first half and was replaced before half time by Philippe Coutinho."
Ahead of Barça's Champions League game away to Dynamo Kiev on Tuesday, interim Barcelona head coach Sergi Barjuan said, "Yesterday I spoke with Kun and he is relaxed. He is locked in his room, but relaxed.”
Aguero's is just the latest heart issue to befall a high-profile international.
Last week it was confirmed that Christian Eriksen would not be allowed to line out for Inter in Serie A this season, following his cardiac arrest which occurred during Euro 2020.
"Eriksen was subsequently fitted with an Implantable Cardioverter Defibrillator (ICD) device, which is a type of pacemaker.
"Medical experts involved in Italian football have said that he won't be permitted to play in the country while the ICD device is in place."