Hamburg coach Markus Gisdol says United States attacker Bobby Wood is in a "negative spiral" and suggested he could soon lose his place in the team.
Wood, 24, stayed at Hamburg in the summer despite links with the Premier League but he has scored just two league goals in the current calendar year.
On Saturday, Wood played for 56 minutes in Hamburg's 2-1 defeat at Hertha Berlin, touching the ball only 19 times in a largely anonymous display. His replacement, 17-year-old Jann-Fiete Arp, then scored just 17 minutes after his introduction.
"We do everything to support him, but we can't do more than we do right now," Gisdol told reporters.