O'Neil has been in superb form for Boro this season and his performances have not gone unnoticed.
The talented midfielder was linked with a move to the Premier League following Middlesbrough's relegation to the Championship, but the Teesside club were able to keep hold of the 26-year-old.
However, a number of sides are ready to test Middlesbrough's resolve to keep O'Neil at the Riverside by launching bids for his services when the transfer window reopens in January.
The likes of Blackburn, Bolton, Wigan, Sunderland, Fulham and Birmingham are all believed to be tracking O'Neil and are ready to firm up their interest in the New Year.
O'Neil's current contract at Middlesbrough expires next summer, unless the club take up a two-year option to extend it.
Middlesbrough are reluctant to lose their midfield talisman and are thought to be demanding a fee in the region of £4million to consider letting him move on.