Nicolas Gaitan, 27, looks to have finalized his move to the Premier League giants after agreeing personal terms.
United have been linked with the Argentine international several times over the last few weeks but a deal is now thought to have been struck.
The player is keen to move to the Manchester club but according to a source close to the club, United need to negotiate an appropriate fee with Benfica for Gaitan.
Reports are emerging Benfica could be offered Nani plus cash to sell Gaitan – the deal could happen sooner rather than later should United part company with Angel Di Maria.
Nani was sent on-loan to Sporting Lisbon – his former club and played a big part in helping them qualify for the Champions League, with seven goals in 27 games.
Meanwhile, former Real Madrid winger Di Maria has struggled to make an impact since his record-breaking £59.7m move from the ten-times Champions League winners.
With just three goals in 27 games for United, there has been speculation manager Louis Van Gaal could decide to offload the winger, with PSG rumoured to be interested.
Written by Jack Wynne – @JackRobertWynne