The new Hoops boss wants team spirit at an all time high.
Ibrox side Glasgow Rangers have already made eight signings so far this summer.
Koeman took charge at Everton after moving from Southampton earlier this month.
The goalkeeper recently agreed to become part of Mark Warburton's Glasgow Rangers side.
The Turkish forward has had an instant impact in Brazil.
The Sunderland manager has been linked with the England job following Roy Hodgson's departure.
The Belgian looks set for a Chelsea switch this summer.
Celtic's Kristoffer Ajer has joined up with the rest of Brendan Rodgers' squad over pre-season.
Batshuayi is poised to complete a £33 million move to Stamford Bridge this summer.
Nottingham Forest have named Philippe Montanier as their new manager for next season.