The transfer of Naldo from Werder Bremen to Wolfsburg is in the balance after the Brazilian defender failed his medical.
Naldo had been set to switch Bundesliga clubs for a fee reportedly in the region of £4.2million in a four-year deal.
But the 29-year-old Brazil international has failed his initial medical with the Wolves and the club are keen to do more tests before committing to the deal.
"We have been getting into a situation we are unable to solve that quickly," Wolfsburg boss Felix Magath told kicker-Sportmagazin.
"At this point in time we are not able to complete the transfer.
"We are still very keen to seal the transaction but we are forced to have a more detailed medical to find out if the player is fully able to give his very best in the years to come."
But Werder Bremen general manager Klaus Allofs has attempted to downplay suggestions the transfer could be cancelled.
"I am expecting the transfer to go through," said Allofs. "I am not surprised, I have to say.
"If you have a medical with a player aged 29, you are always able to identify problems. It's obvious the club will be looking after that."