Techically, he can still play and run, but he might have some pain while trying a cross with the left. (unless the inflammation is big enough, so there can be pain in every step, but in my exp the degree of the inflammation is visible in the ultrasound scan and when they say 1st degree, there is little to no tisue inflammation)
This means minor to no muscular and tendon injury, he only needs to rest some days and do some streches...no rupture, no surgery.
But considering that he is going to use that leg to cross for the rest of his carrier and he is quite the fragile, injury prone guy, i would rest him, just in case, or at least until he is fully recovered, which is up to him.