Julián Álvarez missed Atlético Madrid training for the second consecutive day on Thursday, as the row over a possible move away from the club for the star forward continues.
The Argentina international, 26, was whistled by Atletico fans during their 2-2 draw with Villarreal on Sunday after a summer in which he made public his desire to leave the club and join rivals Barcelona.
Atlético said Álvarez was "unwell" on Wednesday when he failed to join his teammates in training, and a club spokesperson told ESPN that the player continued to feel ill a day later.
Barça president Joan Laporta has reiterated the club's interest in signing Álvarez.
"We're very interested in the player and we'd like our offer to be accepted," he said on Wednesday. "We do so with all respect for Atlético Madrid, and want them to know that if they're willing to sell him in this summer window, we'd be willing to sign him, according to the offer we made."
Atlético then hit back with a statement, saying there was a "zero percent chance" of Álvarez joining Barcelona and calling themselves "victims" in the saga, who had been "damaged financially and socially."
Atlético are next in action in LaLiga on Saturday, when they visit Sevilla.
Álvarez was introduced as a second-half substitute in their game with Villarreal for his first appearance of the season, and was whistled by fans before, during and after the match, before leaving the field alone as his teammates applauded the crowd.
- Álvarez misses Atlético Madrid training due to 'illness'
- Barcelona hopeful of signing Álvarez from Atlético - Laporta
- 10 players who could still move before the transfer window closes
