The Argentine star received the injury when he nicked a ball from Kalidou Koulibaly, when the defender was preparing to clear it long. He accidentally caught Messi with a lot of strength instead of kicking the ball away, and thus gave up a penalty in the process. Both players were on the ground for several minutes after, although thankfully both were able to complete the match.
Luis Suárez scored the penalty afterwards, the third goal in an eventual 3-1 win over Napoli.
The media in Catalonia is saying that Messi’s willingness to go and work with doctors on his day off, to ensure maximum fitness against Bayern on Friday, is a sign that the #10 is extremely plugged in and ready to give his all.