According to this Wikipedia Article, the tennis player was held captive in Castle Itter, but the reason for his arrest is never indicated. Did the Gestapo have a reason to arrest Borotra?
Arrested by the Gestapo in November 1942, Borotra was deported to a concentration camp in Germany and then Itter Castle in North Tyrol until May 1945. He was freed from the castle after the Battle for Castle Itter, in which he played a courageous role by vaulting from the fortress and running to a nearby town to summon reinforcements.
He was arrested at the train station trying to board a train to Spain in order to jump ship to the Allies. He told a friend before he left and was ratted out.