Messi diagnosed with bruised thigh
The Spanish champion says it is still unclear how long he will need to recover from the injury.
Barcelona visits Malaga in the second round of the Spanish league on Sunday.
Messi was substituted at halftime of Wednesday's first leg of the Spanish Super Cup as a precaution after he felt pain in his leg.
The four-time world player of the year missed several games at the end of last season because of a nagging right hamstring strain.