Messi damaged the muscle during Barcelona's victory over Real Betis in La Liga last week, and is expected to be out for six to eight weeks.
The Argentina international has struggled with injuries throughout this year, and his colleague for club and country Mascherano believes the 26-year-old has previously rushed himself back to action too quickly.
And with the FIFA World Cup in Brazil on the horizon, Mascherano has urged Messi to only return when he is 100 per cent ready.
"When we saw Leo lying on the ground and looking at the bench (against Betis), we knew something was up," he told Ole.
"Now he has to be the most selfish person in the world and recover properly.
"Relaxing and taking some time out for himself will do him good.
"Messi is fine. Now he's focused on his recovery. It's a muscle injury, so it's nothing earth-shattering."
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