The Red Devils are refusing to dismiss reports that £60m rated Lukaku is back on Jose Mourinho's summer radar.
United were known to be keen on the Belgium international last year, who earlier this week announced he would not be signing the Toffees' offer of an improved contract renewal.
Mourinho is believed to remain a big fan of the player despite selling the 23-year-old powerhouse when he was in charge at Chelsea.
The United boss also holds a couple of potential aces up his sleeve in Rooney and Lukaku's influential agent, Mino Raiola.
Everton are making no secret of the fact they would love to bring Rooney back to Goodison Park, where it all first began for the 31-year-old United skipper.
And it was Raiola who was last year responsible for bringing Paul Pogba and Henrikh Mkhitaryan to the Theatre of Dreams.
The Italian has earned the trust of the United board and there is increasing chatter in the corridors of power that he can now steer the 25-goal striker in their direction, especially so, if Rooney was part of the equation.