The German winger has been listed on the club's retained list as under contract for next season, after a clause in his loan deal from Union Berlin was activated in the aftermath of promotion to League One.
The 21-year-old made 27 appearances in his first season on Wearside, scoring four goals.
Illness brought his season to an early conclusion, with an issue initially believed to be tonsillitis requiring further tests and treatment in Germany.
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Dajaku did return to training in the build up to the play-off final against Wycombe Wanderers at Wembley and will return with the rest of his team-mates on June 22nd.
Dajaku arrived in August alongside Thorben Hoffmann, but the goalkeeper has returned to Bayern Munich having not made enough appearances to trigger the clause to make his loan deal permanent.
With Anthony Patterson finishing the season strongly, a Wearside return appears unlikely at this stage.