According to an interview with De Telegraaf, Diemers expressed his disappointment at not being able to secure a move to an Eredivisie club, stating: "I wanted to play in the Eredivisie, I think I belong there given my qualities." Diemers' contract with SC Cambuur expired in June after the club only offered him a one-year extension, prompting him to seek a two-year deal elsewhere. VoetbalPrimeur reports that De Graafschap had previously approached Diemers five months prior to his eventual signing.
Diemers also spoke with Telstar before choosing De Graafschap, citing a better feeling about the club and its supporters. He made his debut for De Graafschap against FC Den Bosch and wore the captain's armband in their match against FC Eindhoven, providing an assist in the process.
