Lionel Messi was absent from Barcelona's training session on Wednesday due to illness and was visited at his home by club doctors.
The forward played the full 90 minutes of Barca's 3-1 Copa del Rey loss against Real Madrid on Tuesday evening, but failed to impress as he was kept quiet by the Madrid defence, and he has now been laid low with fever.
"Leo Messi was missing from this morning’s training session at the Ciutat Esportiva Joan Gamper. The Argentinian has gone down with a fever and is feeling generally unwell," a statement on the club's website reads.
"The first team doctors went to his home to check up on his condition, and gave him the appropriate medication and told him he should get some rest.
"The squad has been given Thursday off, and the hope is that Messi will be well enough to join Friday afternoon’s session, the last before travelling to Madrid for the Liga Clasico at the Bernabeu."
Messi has netted 38 goals in 25 La Liga appearances so far this term.