Union Berlin started pre-season training on Wednesday with top striker Taiwo Awoniyi only making a brief appearance to bid farewell to the other players and staff.
The 24-year-old Awoniyi is linked with a move to promoted English Premier League club, Nottingham Forest.
Awoniyi, who scored 15 Bundesliga goals for Union last season, reportedly has a 20 million euros ($21.1 million) release clause in his Union Berlin contract.
The team’s coach, Urs Fischer, did not have a full squad available on Wednesday, after performance tests the previous two days, as several national team players are still on holiday.
Newly-signed Danilho Doekhi from Dutch club Vitesse is to join the squad on Thursday.
The two arrivals from relegated Greuther Fürth, Paul Seguin and Jamie Lewelling, were also not present on Wednesday.
Defender Timo Baumgartl, whose loan from PSV Eindhoven was extended for another season, is set to join the squad next month after undergoing treatment for testicular cancer.
Union Berlin start the Bundesliga season with a home game against crosstown rivals Hertha Berlin on the weekend of August 6 and 7.