Chelsea have signed forward Pierre-Emerick Aubameyang in a £12m deal from Barcelona with defender Marcus Alonso expected to go the other way.
The 25-year-old Swiss international would boost Chelsea's midfield options.
Gabon international Aubameyang scored 13 goals in 24 appearances for Barca after joining the Spanish club in February from Arsenal.
The 33-year-old had a buyout clause of 100m euros (£83.4m) in his contract, but has only played eight minutes this season.
Aubameyang scored 92 goals in 163 games in all competitions for Arsenal, but left on a free transfer after falling out with manager Mikel Arteta.