Chris Rigg's first professional contract hasn't put an end to transfer speculation. The Sunderland youngster continues to attract attention from some of the Premier League big boys after his scintillating form this season.

Man United, Newcastle United and Everton have all been linked with the 17-year-old. Crystal Palace are also interested in the midfielder who has previously drawn admiring glances from around Europe as well.

But what could the Sunderland youngster be worth in the current market? And while Sunderland will be loathe to lose a player who will undoubtedly play a key role in their future, what could Rigg be worth if the transfer interest intensified?

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According to Transfermarkt, Chris Rigg was valued at only £300,000 before the start of the current season, but their valuation has since rocketed with his impressive form seeing that figure rise to £12million at the beginning of the January transfer window. Evenn then, however, that feels cheap.

Sunderland have fended off interest in Tommy Watson this window, with Brighton having an £8.5m bid for the winger rejected. Sunderland are believed to value him at £10m as Palace and Aston Villa also keep tabs on his progress.

Rigg - despite being a year younger - has much more experience than Watson and is further ahead in his development, having made his debut aged just 15. Jude Bellingham is perhaps the most relatable to Rigg as he made a move from a Championship side in Birmingham City, joining Borussia Dortmund for a fee which would stand at around £25m at the current exchange rate.

He had made a similar number of senior appearances to Rigg at the time of his departure, which could make it a fair comparison. Interestingly, Transfermarkt had Bellingham valued at around £8m when he completed that move.

Other players to have moved from the Championship at a young age include Adam Wharton, who signed for Crystal Palace for a reported initial fee of £18m, and Alex Scott - who swapped Bristol City for Bournemouth for £25m.

Looking further afield, Gareth Bale made the move from Southampton to Tottenham in 2007 at the age of 17 for around £12m, while Brazilian Alexandre Pato left his homeland at the same age and joined AC Milan in a deal worth close to £20m.

While it's hard to predict what trajectory Rigg's career will follow, the potential is certainly there. And that - coupled with his long-term contract on Wearside - certainly would allow Sunderland to drive up his valuation based on these previous deals should they wish to cash in on him at any point. Anything less than £25m surely wouldn't be entertained.

Not that head coach Regis Le Bris is contemplating such a move. Instead, the Frenchman is excited at the prospect of welcoming Rigg back into his starting XI tonight against Middlesbrough. Rigg has been suffering with an ankle injury but could return for the Teesside clash, having appeared as a substitute last time out against Plymouth Argyle.

"For such a young player, he is so consistent," said Le Bris. "When we do the post-game analysis, you are trying to find the small details. With Chris, we understand that he is very talented with the ball, he can create many things and his left foot is very good but out of possession, he is just as important for the team. That is because he is very smart and also intense.

"Sometimes it is difficult to assess the importance of a player game after game. But when Chris is not on the pitch, it becomes clear. A few weeks ago, he struggled with an ankle injury and missed two or three games. We had to change the structure and at that moment, we could feel that the role he had was so well done.

"We could feel his lack of presence so yes, so far he is really impressive. It is clear we are better with him playing."