Koeman also confirmed that he has not considered a move to sign Ajax goalkeeper Kenneth Vermeer, who is expected to join Feyenoord.
He added: "We didn’t think about Kenneth Vermeer. We have bought Fraser Forster, who is 26 years old and a fantastic goalkeeper, who is part of the England squad."
The Dutchman also acknowledged that deals for Aston Villa defender Ron Vlaar and Dynamo Kiev forward Jeremain Lens ‘didn’t succeed’, and that he opted against an approach for Queens Park Rangers new boy Leroy Fer due to the number of midfielders already at his disposal.