The Gambian winger came to Öster before last season and has impressed greatly in the beginning of Allsvenskan with his speed and technique.
Expressen has previously stated that Öster receives 32.5 million kronor plus potential bonuses of 5.5 million. Öster does not disclose any transfer fee but writes on its website that the deal is a new transfer record for the club.
"We are proud to make a deal of this magnitude. It has been a process that has been conducted in a positive dialogue with Slavia Prague over time and now we have reached an agreement that both parties are satisfied with. This is a big day and a milestone for Östers IF", says Christian Järdler, acting sports manager in Öster.
According to club director Jens Magnusson, the deal "will ensure the economy for the association over time".
Öster is in a qualifying spot in Allsvenskan after twelve rounds.
