Everton midfielder Barkley, who has one year on his contract remaining, was left behind for Everton's trip to Tanzania due to an injury.
However, Tottenham lost their interest in signing him, due to Everton's £50 million asking price. Arsenal and Chelsea have also shown interest in Barkley, but the Toffees won't let him go cheaply.
Everton have already signed midfielder Davy Klaasen and are also trying to sign Glyfi Siguardsson, which would mean that Barkley would have to fight to get into Koeman's starting lineup.