Diop has emerged as one of the stars of Senegal's brilliant showing at the World Cup, and United have faxed both his agent and his French club Lens to inform him of their interest.
However, the player does not yet qualify for a work permit, so any deal will have to be put on ice until the New Year.
"Lens and I have a fax from United informing us officially that the English club are interested in Bouba.
"For the moment Bouba cannot yet play in England as he hasn't played a sufficient number of games for Senegal to get a work permit.
"So he won't have a chance to play in England before January."
Diop scored the historic opening goal of World Cup 2002, which proved to be the winner against holders France - in one of the biggest ever shocks in the tournament.
But the midfielder did not rest on his laurels and scored two more in the group game against Uruguay, confirming his place as one of the stars of the tournament.
United's interest, should it prove to be true, is an indication that manager Sir Alex Ferguson is still looking to bolster his squad.
The Red Devils relinquished their hold on the Premiership title to Arsenal last season, but are desperate to wrest back domestic dominance from the London club.
