Manchester United have reportedly submitted a £21.5m bid to Borussia Dortmund to acquire the services of defender Mats Hummels.

According to the Daily Mail, the Bundesliga club value their defender at about £35m and will let the defender leave for the right price this summer.

Louis van Gaal has made strengthening his defence a priority in the summer, and the German World Cup winner is the Dutchman's preferred choice to fill the void left by the departures of Rio Ferdinand and Nemanja Vidic.

Hummels has already admitted that he is keen to move abroad to further his career and he has been urged by many former players to make the switch to Old Trafford in the summer.

The 26-year-old defender, who was the rock of the Germany team that won the World Cup, has had a mixed year as Dortmund have struggled in the Bundesliga. With the recent announcement of Jurgen Klopp's departure at the end of the season, it is likely that the German will depart the club.

But the club's hierarchy have made it clear that the decision on Hummels' future will be taken by Borussia Dortmund once they receive a satisfactory offer.

Following the reports regarding United's first bid for the defender, German newspaper Bild contacted the club's sporting director Michael Zorc, but he refused to confirm the same.

"I can not confirm this!" Zorc said, as quoted by the Bild.

Even Hummels was contacted regarding the latest offer, but the defender refused to deny or confirm the same stating that he has nothing new to add to the comments he made earlier in the season regarding his future.

"I have no desire to express myself constantly new to this topic. I've done a few weeks ago - that must be enough! " Hummels reiterated.