Messi aggravated a hamstring problem on international duty and has been told to modify his training regime amid uncertainty over whether he will face Alaves on Saturday. Barca then host Celtic next Tuesday in the Champions League.
A statement on their official website read: "Tests conducted today on Leo Messi have confirmed that the player is still having trouble with the adductor muscle in his left hamstring. He has been recommended to lighten his training load over the next few days and his availability will depend on how the issue progresses."
Messi has scored four times in five competitive games this season, including the only goal in Argentina's World Cup qualifier against Uruguay.