Radio RAC-1 says Messi refused to train immediately after the 4-0 win, when he was substituted by coach Pep Guardiola for young striker Pedrito. Messi was unhappy with the decision and remained angry the next day.
Initially, Messi was ready to snub the morning training session, but eventually was convinced to go by friends after a series of frantic phone calls. However, while at the Nou Camp, Messi refused to change into his shorts and instead spent the session in the locker room watching television.
Later, Guardiola settled the issue with Messi.
Barca explained his absence officially as "he was doing therapy". It has not transpired, however, if the club fined Messi.