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

Borussia Dortmund defender Mats Hummels has informed the club he will take time to consider his future amid mounting speculation suggesting Manchester United will move for the defender this summer.

Hummels, 26, remains a long-term target of the Old Trafford club with recent reports suggesting the club are planning to move forward with a bid of £36m at the end of the season.

Dortmund's disappointing campaign - the club currently sit 10th, 31 points behind leaders Bayern Munich - has helped fuel talk suggesting the Germany international will seek a new challenge at the end of the season.

But while the club have been told their captain will consider his options, they are 'completely relaxed' over his future.

Dortmund CEO Hans-Joachim Watzke told Bild: "Mats held talks with me and [sporting director] Michael Zorc 14 days ago, and informed us that he is mulling over his future," ESPN report.

"That is totally legitimate.

"He is under contract until 2017, and we have not received an offer. That is why we are completely relaxed."

Talk of Hummels joining United at the end of the season was also intensified following the emergence of a report in Bild which suggested the centre half had previously promised that the only club he would leave Dortmund for would be United.

Hummels however denied ever having made such a promise, taking to Twitter to condemn the 'fictitious' story.

United boss Louis van Gaal is expected to bring in an established defensive presence to lead his younger options at centre half this summer.

World Cup-winner Hummels was heavily linked with such a move to Old Trafford last summer, but Dortmund's decision to name him their new club captain following Sebastian Khel's decision to step down as skipper briefly ended talk of such a move.