The Belgian midfielder spent two months with the League Two leaders and made nine appearances. He's now back with Blues and will go straight into the squad for the Boxing Day clash at home to Northampton Town.
Speaking to the Southend Evening Echo Blues boss Steve Tilson said: "It was good for Franck to go out and some get some games with Wycombe. It's helped his development as a player and he's been involved in a winning mentality at Wycombe. Hopefully he can bring that back with him to us now."
Moussa, 19, has made 30 appearances for Southend since emerging through the club's youth system but he has not played for Blues since being sent off against Brighton in late August.