Neven Subotic will not be joining Middlesbrough due to a rib injury detected during medical tests, Borussia Dortmund have confirmed.
Reports emerged early on Wednesday that the centre-back's proposed transfer to the Premier League was off after he failed a medical at the club, though his agent denied that any such decision had been taken.
However, the Bundesliga club have now announced that the 27-year-old requires surgery, which rules out any possible transfer and is likely to keep him out of action until the new year.
"Bad news for Neven Subotic. A specialist has found out that the Borussia Dortmund defender needs surgery on his ribs," a club statement, released via Twitter, confirmed.
"He will miss the rest of the year and there will therefore not be any transfer for him during this period."
Subotic has been blighted by injuries in the past two years - the latest a thrombosis problem with his arm - and made only six appearances in the Bundesliga last season.