Blades manager Paul Heckingbottom says the 34-year-old has recovered from the thigh injury which ended his season early, allowing Boro’s Chris Wilder to sign him as a free agent for a second time in four years.
Malmo centre-back Anel Ahmedhodzic is reportedly the Blades’ top defensive target in a window yet to bring new faces.
The Bosnian was loaned to Bordeaux last season and as they were relegated two divisions over financial issues, a permanent move seems impossible but the 23-year-old is not available until the option to buy expires.
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Former coach, Jon Dahl Tomasson – now at Blackburn Rovers – is expected to bid too.