Hertha Berlin have said John Brooks' early return from international duty with the United States "raises a few questions," with the defender in danger of missing Sunday's key game at Borussia Monchengladbach.
Berlin-born Brooks, 23, faces a race against time to feature for third-placed Hertha at fifth-placed Gladbach.
He returned to the German capital on Sunday for a scan on the injury, which revealed only bruising and raised the possibility of him being fit in time for the Bundesliga clash.
He took a knock in Hertha's 2-1 win against Ingolstadt on March 19 but departed on international duty the following day.
Hertha sporting director Michael Preetz told kicker: "It was all a bit curious and certainly not ideal.
"John boarded the plane without any acute problems and returns injured. It raises a few questions."
Preetz added, however, that Brooks might have "underestimated" his injury from the Ingolstadt match.
He said: "It might have made sense to keep him here in Berlin for one more day to see how things developed.
"Instead, he now has 30 flight hours in his bones. And the U.S. association keeps him on site for four, five days without any real examination."
The player's agent, Kadir Ozdogan, also told kicker: "I can't imagine that he didn't receive the treatment he should have received."