A statement published on Chelsea's website announced the 18-month loan deal for Rahman and also said Brazilian forward Nathan had moved to Belenenses in Portugal on loan until the summer.

Rahman, 23, joined Chelsea from Augsburg as a promising left-back, but only made 23 appearances for the Blues in 2015-16.

The Ghana international made 21 appearances on loan at Schalke in the 2016-17 season before his campaign was cut short by a cruciate ligament injury while in action for his country at the African Nations Cup last January.

The left-back is the third player to join Schalke this summer. The Bundesliga club have already completed a loan deal for Marko Pjaca from Juventus and the transfer of Cedric Teuchert from second-tier side 1.FC Nurnberg.