Yoenis Cespedes injured his right quadriceps on July 9 against the Washington Nationals. From then until he went on the DL on August 3, he was in and out of the lineup and clearly not playing at full strength.
Yes, Cespedes is the key cog in the Mets’ offense, and it is very difficult for them to score runs when he does not play. However, a month after the injury, Cespedes clearly had not healed, and the Mets essentially lost a month of their slugger’s best services (which will now be six weeks with the DL stint), when he could have been back in as little as two weeks had he been disabled immediately.