Mats Hummels
Hummels has told Dortmund he is mulling over his futureReuters

Manchester United have received a massive boost in their pursuit of Borussia Dortmund defender Mats Hummels after CEO Hans-Joachim Watzke confirmed that they are open to letting the defender leave should a respectable offer come their way.

The Germany international has been heavily linked with a move to Old Trafford over the last two transfer windows where he has refused to entertain any talks about an exit.

However, with Dortmund struggling to finish in the top four and running the risk of missing out on Champions League football, a transfer is back on the cards for the 26-year-old.

Louis van Gaal is a huge fan of the defender, having worked with him during his time at Bayern Munich, before letting him leave as a teenager.

His addition will add the much needed strength and experience to the United backline, which has flattered to deceive this season and have been saved on multiple occasions by the genius of David de Gea, who has been a revelation this season for the 20-time Champions.

United are yet to make an offer for the player, whose contract expires in 2017 but Watzke insists that any offer will be carefully scrutinised before reaching a decision.

"In this moment, this a total dummy discussion, because there is no offer. If one arrives, we will discuss it internally and make a decision. But this decision will only be taken by BVB," Watzke said.

"The situation at Dortmund is like this: We've lost one major player each year, but we don't stop playing football.

"To be clear: Mats knows his contractual situation, he described it in that interview himself. The decision where Mats will play next season will only be taken by BVB," he added.

The defender is valued at upwards of £36m which shouldn't be an issue for United given their financial prowess.

Watzke also insisted that the club is not under compulsion to sell, which they have shown in their treatment of Robert Lewandowski, who they let go on a free after the player refused to extend his contract.

"If we had sold Robert, we maybe would have got €25 million. But we kept him and got €50 million more. This is the same issue here.

"We're not thinking about the short-term. You only do that if you need money and that is not the case with us," Watzke added.