The Frenchman has had a solid campaign with Frankfurt this campaign. He has bagged 19 goals and eight assists in all competitions.
Frankfurt want a package of around €80m for his sale, considering they reportedly owe 20 percent of the sell-on fee to Paris Saint-Germain.
The price could reportedly increase if he continues to impress this term.
Meanwhile, United are one of the clubs who are really hot on the player, but it remains to be seen whether they can afford his signature.
The club are not in a position to pay such a fee at the moment, but the scenario could change if they were to win the Europa League.
Otherwise, the Red Devils could concentrate on landing Ipswich Town's Liam Delap, who could be signed for less than €50m due to a release clause.
United are set to face competition in the pursuit of either player.