The 18 year-old, left sided midfielder has not featured in the first team so far this season but Hammers boss Alan Pardew has requested that Cohen not be played in any domestic cup games.
Yeovil’s boss Steve Thompson told their official website, “We've signed Chris because I felt that we only had three central midfielders at the club in a squad of 26 and we need some cover in that position.
“It also gives both ourselves and Chris the opportunity to look at each other during the month, which is a good thing.
“Every player brought in on a month's loan is with a view to a permanent move because if a player comes in and impresses during that month, the chances are you may well want to sign him.
“Obviously, though, it all depends on West Ham as well.
“They didn't want Chris cup tied which shows that he is not that far away from the team and highly rated.”