The 29-year-old Australia international made only 21 appearances, scoring seven goals, for Middlesbrough last season after his £4.5m move from Leeds, and played just 10 minutes of football after Christmas.
Viduka formed a partnership with another ex-Leeds favourite Jimmy Floyd Hasselbaink but his lack of match action proved disappointing.
Toon boss Graeme Souness would have to be certain of his fitness before he could formalise any interest however.
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