According to Sky Sports News, Dembele is on United's shortlist should Lukaku leave for Inter Milan this summer.
Inter have already had a £54 million bid rejected by United last week, who are holding out for closer to £79m.
Inter chief executive Giuseppe Marotta is aware that in order for Inter to fund a bigger bid for Lukaku, players must be sold to comply with Financial Fair Play regulations.
Dembele, 23, is thought to be considered a pure No.9 by United, and therefore more suited than someone like Lille's Nicolas Pepe, who has also been linked but looks likely to join Napoli.
Frenchman Dembele was a hit in Scotland at Celtic, and last season managed 23 goals in all competitions for Lyon.
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