Cape Town - Manchester United have reportedly tabled an opening offer of £21.5 million for Borussia Dortmund star defender Mats Hummels.
The Red Devils have sought to test Dortmund's resolve with a firm offer, according to German publication Bild.
In March, the Germany centre-back Hummels told German magazine Kicker that he "often thinks about moving abroad" and told German daily Bild a far stronger indication of his Manchester thoughts.
"If I was to transfer abroad at some stage, then it would only be to Manchester United," Hummels is reported to have said.
The German defender who is also a target for Liverpool is expected to follow Jurgen Klopp out of the door at Dortmund this summer.
Hummels' current deal expires in June 2017.