Barcelona striker Sergio Aguero will be out for three months after suffering chest pains during Saturday’s match against Alaves.

The 33-year-old striker was withdrawn before half-time after receiving treatment for several minutes during the La Liga game at the Nou Camp, and underwent cardiac tests at hospital as a precautionary measure after leaving the ground in an ambulance.

In a tweet, Barcelona said: “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.”

Barcelona caretaker coach Barjuan said Aguero was “calm” after speaking to the player, who remains in hospital.

“I talked to him and he’s calm. He’s confined to his room but considering the situation he’s calm,” Barjuan said on Monday.

Aguero’s old team Manchester City sent a message of support and wished the Argentine well, likewise former team-mate Raheem Sterling.

Meanwhile, Barjuan will oversee his first Champions League match as interim boss in Tuesday’s Group E clash against Dynamo Kiev and knows his team are under pressure in Europe.

Barca are third in the standings with three points from three games, a point behind Benfica and six adrift of group leaders Bayern Munich after being thrashed 3-0 by both teams.

They got up and running halfway through the group stage with a 1-0 home win over the Ukrainian side last month and must now claim another three points in the return match in Kiev as they bid to finish in the top two and reach the knockout rounds.

“Barcelona have to win always. But we all know the importance of tomorrow’s game,” Barjuan told a pre-match news conference on Monday.

“It’s my obligation to squeeze the best out of my players and they have to believe they can turn things around and I see this game as a great opportunity to do it.

“They need to play with order and intensity but we should not be nervous. We play better when we are calm and composed.”

The former Barca player moved up from the B team to take charge when Ronald Koeman was sacked on Wednesday after a second consecutive LaLiga defeat – 1-0 by Rayo Vallecano.

“It’s an honour to coach Barcelona in a Champions League game. I did it as a player but it’s different. We still depend only on ourselves to go through, so we need to do our best to go back home with the win,” added Barjuan.

Ansu Fati, Ousmane Dembele and Frankie de Jong took part in training on Monday after coming back from injuries and will make the trip to Ukraine, though Barjuan did not say if they would start.

“It’s an important game to all of us and the players need to be 100 per cent, physically and mentally. We will see how they look on gameday and adjust,” he added.