Feverish Messi misses Barca training
"Leo Messi was unable to train as he had a bad night due to a fever," the club said on their website.
"The Argentine came to the training ground to consult with club doctors and then returned home to recuperate," they added.
The World Player of the Year, who was unable to add to his tally of 18 league goals on Sunday but was again instrumental in Barca's victory, will miss Wednesday's King's Cup quarter-final, second leg at Real Betis if he fails to recover in time.
Coach Pep Guardiola is in any case likely to rest Messi and a host of other first-choice players as La Liga leaders Barca have a 5-0 advantage from last week's first leg.