Sporting Lisbon midfielder Bruno Fernandes's move to Manchester United is reportedly being held up by an unusual compensation clause contained in his contract.
United have been tipped to wrap up a deal for the Portugal international ahead of the January 31 deadline, despite rumoured competition from rivals Manchester City.
The Daily Record suggests that the Red Devils' initial offer of £50m has been structured around a clause that entitles Fernandes and his agent Miguel Pinho to a €5m (£4.27m) payment that must be paid in full.
United are said to have included a number of performance-related bonuses in their offer to the Portuguese club, including one-off payments if they win the Premier League or Champions League.
Ole Gunnar Solskjaer's side have upped their search for a new attacking option following the loss of Marcus Rashford to a back injury that will rule him out for around two months.
Dinamo Zagreb's £21m-rated midfielder Dani Olmo is believed to be another option for United.
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