Moises Caicedo and Romeo Lavia could make their debut for Chelsea on Sunday.
The Blues have wrapped up deals for both midfielders even though Liverpool was in the running for both players.
Chelsea have now found a perfect midfield partner for Enzo Fernandez but manager Mauricio Pochettino is in no rush to throw the duo straight into the first-team.
The players have been registered in time to be available for West Ham but Pochettino will refuse to hand debuts if the duo are not physically prepared.
Both Caideo and Lavia will be assessed before the game and the final decision will be taken by the Argentine manager.
“We have one day more to assess them, but it has been stressful weeks for Moises and Romeo also,” he explained. “It would be easy to say they would be involved but the most important thing is to avoid risks and not to rush with them.
“If they are ready tomorrow, they will be involved but if not, we will wait a few days more to be involved in the squad.”