Borussia Dortmund defender and Middlesbrough target Neven Subotic is likely to be out for the rest of 2016 as he requires surgery on a rib problem.
The Serbia international missed the end of the 2015/216 campaign after he was a diagnosed with thrombosis in his arm.
Subotic had been linked with an £8m move to Middlesbrough and was shown around the club's facilities earlier this month.
The deal came to nothing, however, and the 27-year-old now faces an extended spell on the sidelines following a consultation with a specialist in England.
Subotic has made 172 appearances for Dortmund, winning two Bundesliga titles and the German Cup during his time at the Westfalenstadion.