The Foxes signed 21-year-old Casadei on a temporary deal in the summer, following a number of appearances for Chelsea in pre-season.
In six months at the King Power Stadium, he has scored three goals in 25 appearances but only started eight league games for the Championship leaders.
Mauricio Pochettino will welcome Casadei back to the first-team squad ahead of the cup games against Middlesbrough and Aston Villa after Chelsea's winter break from Premier League action.
A number of injury issues continue to affect the Blues with midfielders Lesley Ugochukwu and Romeo Lavia currently unavailable.
The middle of the park is an area of the pitch where Chelsea lack as much depth as other areas, with Carney Chukwuemeka the only natural centre-midfielder named on the bench for the recent win over Fulham.
The club have sanctioned loan moves for Ian Maatsen and Alex Matos during the January transfer window but want to keep young right-back Alfie Gilchrist. Full-back Dylan Williams and goalkeeper Lucas Bergstrom are thought to be available for exits on loan before the deadline.