Real Madrid have reportedly hit a stumbling block in their efforts to sign Porto defender Eder Militao.
The young Brazilian only moved to the Portuguese giants in the summer, but the 21-year-old's form and release clause has resulted in widespread interest in his signature.
Real appear favourites to get a deal over the line, having shown that they have prepared to meet the desired fee and having agreed personal terms with the player.
However, according to Marca, a transfer failed to go through during the January transfer window due to a dispute over a training fee.
Compensatory training fees can be demanded when a player has been trained between the age of 12 and 21, and Porto allegedly feel that they are entitled to €6m (£5.25m).
The report suggests that Real do not feel obligated to pay the fee, and discussions are likely to continue in an attempt to find a resolution.