According to ExWHU/West Ham Way:
Following a social media post it appears that Dutch winger Crysencio Summerville has had an operation on his injured hamstring. The player has been out of action since the Aston Villa cup game. The player had wanted to avoid surgery and heal naturally but it seems that he has now reluctantly had the operation.
We have asked a top source at the club for comment and we will update this post once we have received it. The post does confirm that the player is now officially out for the rest of the season.
Update 1: We can exclusively reveal that due to waiting longer for the operation than needed, the operation was now a much more complicated operation than it would have been before. The initial verdict is that he will be back in mid August at the earliest, now as a result.