Immediately following their 3-0 loss to Manchester City on Sunday, Chelsea announced the signing of FC Augsburg defender Baba Rahman on a deal reportedly worth near £20million.
"I am very happy to sign for Chelsea, one of the biggest clubs in the world, and I can't wait to train with my new team-mates and very much looking forward to working with them and Mr Mourinho," Rahman told the club website.
"I am also looking forward to having the opportunity to meet the fans as soon as possible."
The 21-year-old Ghana international spent only one season in Augsburg, where he helped lead the club to a Europa League spot after making 31 appearances in the Bundesligha last year.
Rahman's arrival gives Chelsea cover at left-back after the departure of Filipe Luis and the defender can also play in midfield and along the wing.
