The 20-year-old has also moved to the Gallagher Stadium for the remainder of the season to help a squad which is currently stretched following the departure of Zavon Hines and Joe Pigott and injuries to Tom Wraight and Jamar Loza.
Coker has been a regular in Palace`s development side for the past couple of seasons, and regularly chips in with goals and assists.
The local lad, who can also play as a striker, is a strong, powerful player who has been at the club since he was 13-years-old and is now a regular for the Eagles under-23 side.