NEVEN SUBOTIC’S transfer to Middlesbrough has broken down, with Borussia Dortmund this evening admitting the defender requires rib surgery that will keep him out of action for at least six months.

Subotic had been expected to join up with the Boro squad in Marbella this week after an agreement with Borussia Dortumund over a fee was reached last week.

But Subotic’s move, which was due to be for an £8m fee, collapsed this morning amid speculation that the centre-half had failed a medical on Teesside.

Subotic's representatives initially denied the claims, but Borussia Dortmund have subsequently confirmed that medical issues are behind the collapse of the proposed deal.

The Dortmund statement said: "Bad news for Neven Subotic.

"The investigation of a specialist in England has shown that the Borussia Dortmund player must undergo surgery in the rib area.

"It is expected that Subotic will be out for the rest of the year."

Subotic would have been an exciting signing ahead of Middlesbrough's return to the top-flight, and the club will now be looking for other defensive reinforcements ahead of the visit of Stoke on August 13.

Head coach Aitor Karanka, whose side lost 2-1 to Real Betis in Marbella on Tuesday night, has already made eight new signings, with Valencia striker Alvaro Negredo the latest player to have been confirmed this afternoon.

But Karanka has been left frustrated in his hopes of landing Subotic, who is known to have been impressed by what he has heard and seen during his time being shown around the Teesside club’s facilities.

Middlesbrough had hoped to confirm the deal at the beginning of this week and club sources had suggested everything had been concluded with the exception of his work permit application.

There were doubts surrounding whether he would receive the permit, although Middlesbrough were confident that they would be able to secure one given his standing within the European game after a successful spell with Dortmund.

Arsenal, Liverpool, Sunderland and Everton had all been linked with Subotic, who Dortmund boss Thomas Tuchel had been happy to sell on this summer.

The Serbian suffered from a thrombosis in his left arm last season, which limited his availability for Dortmund.