Scott McKenna will fly to Croatia with his Aberdeen team-mates two days after handing in a transfer request.
The Scotland defender, 22, expressed his desire to leave Pittodrie amid interest from several English clubs.
Aberdeen have already rejected bids from Queens Park Rangers and Nottingham Forest for McKenna this summer.
Derek McInnes’ side face Rijeka in the first leg of their Europa League third qualifying round tie on Thursday, and McKenna is among the travelling party.
The centre-back, contracted to 2023, has played five matches this term, including Aberdeen’s Scottish Premiership opener, a 3-2 home win over Hearts on Sunday.