In FM these kind of Kephren and Weah injuries is the one with orange colour, and always happen if you choose heavy training pre season especially if you forgot to change the rest tab when they fit you push them for double session.
Only need to put them aside for awhile and they will comeback stronger and more injury free throughout the season. But too bad in real life this kind of injury need 2-3 weeks for recovery. While in FM it is usually they will back 1 day before the next match (I dont know how they can be so precise with this timing of this kind injury)