One tough match and he's injured?
As any athlete knows, it only takes one wrong step, or an over extension to the shoulder, etc. to incur an injury. So certainly a tough match can generate new or aggravate previous injuries.
As much as some would like them all to be indestructible automatons, they are still made of flesh and blood.
It wouldn't surprise me to see Mr. Djokovic or Mr. Nadal unfortunately suffer injuries by the end of Roland Garros, or earlier if they continue playing as they have.