The 21-year-old was snapped up by the Toffees in the summer after they initially beat United to secure his signature.
As soon as he arrived at Goodison Park he was sent out on loan to Belgian outfit Anderlecht.
And he has thoroughly impressed since moving to the Constant Vanden Stock Stadium, scoring seven goals in 14 games.
Anderlecht sit third in the table, nine points behind leaders Club Brugge.
And there had been talk of Everton recalling him as they continue to struggle following the sale of Romelu Lukaku.
According to Dutch publication HLM, United and Barcelona sent scouts to Anderlecht’s 2-1 victory against Royan Excel Mouscron.
Onyekuru struck the winning goal and would certainly have caught the eye of the watching brief.
The report also states that Southampton, Stoke, Ajax and PSV Eindhoven are also interested in the Nigerian
Onyekuru recently made his international debut during a 1-1 World Cup qualifying draw against Algeria.
And he looks almost certain to be in the squad for the World Cup in Russia next year.
But it is not clear if Everton will be able to keep hold of the forward if Europe’s elite come knocking.