The centre forward has been outstanding so far this season, scoring 15 goals in nine Bundesliga games.
The experienced attacker, per Mercato, may be the one United turn to in a bid to rescue their season.
Guirassy would be an affordable purchase to provide depth in attack and help in the quest to score more goals in the Premier League.
Guirassy has a £15.1 million release clause that would make negotiations very easy for United.
The question is whether the club believes he is good enough as a long term first team player.