Mats Hummels
Dortmund's Mats Hummels now has two suitorsReuters

Manchester United are in danger of missing out on Borussia Dortmund defender Mats Hummels after Barcelona joined the race for his signature, according to reports in Germany.

The 25-year-old ‒ who joined Dortmund initially on loan from Bayern Munich in 2008 ‒ later cost them just £3m and the club could make a tidy profit on the player. But Borussia look as if they are unwilling to let any of their star players leave over the summer after already having lost Robert Lewandowski on a free transfer to the Bavarian giants.

But Barcelona are looking to strengthen their defence, following the retirement of veteran captain Carles Puyol and, according to the Express, the Catalan club have joined United in race for Hummels as both clubs need reinforcements for their defensive lines – even though Barcelona's main target is Paris Saint-Germain's Marquinhos.

It was reported that the Brazilian wants to sign for the Catalans in the summer as his first appearances are likely to be limited next season with David Luiz's arrival at Paris.

Earlier this week, it was reported that Manchester United are set to make a £20m offer for the defender as the Red Devils are in the market for defensive reinforcements to cover the departure of their two experienced defenders Rio Ferdinand and Nemanja Vidic.

However, Hummels recently claimed he is happy in Dortmund but has admitted that a move to United could appeal to him "someday." If his club accepts the fee, the German defender could be tempted to a move across to England and specifically to Old Trafford.

Hummels is currently in Brazil with the German squad and is proving one of the key members of Joachim Low's team.