Middlesbrough are facing the prospect of a massive summer in the transfer market.

Neil Warnock has made no secret of his desire to make huge changes to the playing squad as he looks to move a handful of players on and replace them with individuals who are capable of guiding the club to promotion.

Doing that, however, could be tricky.

Part of the summer rebuild could come down to sell on first team players.

The club have worked hard in recent years to sign young, talented players who could potentially be sold on for a profit in the future.

But which players have seen their value increase the most since first appearing for the club?

Here are the top 10 Middlesbrough players who have had the biggest market value increases since their debuts, according to Transfermarkt.

The winger completed a move to Middlesbrough back in the summer of 2017 when he joined from Oxford United.

Since signing for the Teessiders Johnson has made 99 appearances for the club, scoring seven goals and creating 13 more for his teammates.

At that time his market value was said to be a £450,000 which rose to £1.8million the following year.

However with the 30-year-old's contract currently coming to an end this summer it has seen his market value drop slightly from that amount.

At this point Johnson is worth £1.35million which means that his value has increased by £900,000 since joining the club.

The midfielder is regarded as one of Middlesbrough's most important players.

McNair moved to the Riverside Stadium in August 2018 after suffering relegation to League One with North-East rivals Sunderland.

At the time of that move he was valued at £2.7million with his current value now said to be £3.6million.

That means that the Northern Ireland international has increased by £900,000 according to Transfermarkt, however I'd be very surprised if Middlesbrough would entertain selling him for an amount as small as that.

The left-back has certainly been one of Middlesbrough's real success stories this term.

Bola arrived at the club from Blackpool in the summer of 2019 with the player valued at just £90,000 at the time.

Despite a frustrating first campaign with the club, the 23-year-old has really kicked on this season and is now a regular feature in Neil Warnock's starting XI.

It's thought that Bola is now valued at £1.08million, meaning that his value has increased by £990,000.

While that may be his market value there's no doubt that Middlesbrough would value him much higher if someone was to make a move.

Another left-back who has seen his value grow significantly since making his first team debut.

Coulson is a product of Middlesbrough's youth academy which means that his value was just £90,000 when he made his first appearance for the club.

Since then the 22-year-old has really kicked on and is seen as a valuable part of Neil Warnock's squad.

While his future may be hanging in the balance this summer, it's claimed that Coulson is now valued at £1.08million which means he's price tag has increased by £990,000.

Given that he's a product of the academy he's a player who could make the club a hefty profit if he was sold on.

Another player who has really emerged as a first team player during the last year or so.

Spence started his youth career with Fulham but completed a move to Middlesbrough in search of better development opportunities.

The right-back made his first team debut in August 2018 when, according to Transfermarkt, his value was nothing.

It's safe to say that this is no longer the case with the player a regular part of Neil Warnock's plans at the Riverside Stadium.

Spence is now said to be worth £1.8million which means that his value has increased significantly in his short time at the club.

A player who may well be leaving the club for nothing this summer.

Fletcher joined the club in the summer of 2017 and was valued at £900k when he made his first Middlesbrough appearance in August that year.

The fact that Middlesbrough paid £6.5million for the player is an argument for another day.

While injuries have stopped him from really kicking on the striker has been a big player for Middlesbrough in that time and is now valued at £2.7million, meaning that his valued has increased by £1.8million.

Unfortunately his contract situation suggests that the club won't be making anything like that figure if he moves on this summer.

The defender is another player who has really kicked on this summer.

After arriving from Charlton in the summer of 2019 Dijksteel struggled to make an impact in his first campaign with the club, but this season he has really kicked on.

Dijksteel is now a first team regular under Neil Warnock and that his seen his value increase from nothing to £2.25million, meaning that the entire sum is an increase.

Given how much he's improving I'm sure that Middlesbrough fans will be hoping that he can kick on even further.

The midfielder arrived from Milwall for a significant fee back in the summer of 2018.

Since then the jury has been out on George Saville with many unsure whether his addition has really been worth the money that was spent on him.

It's said that his market value was just £1.35million when he made his debut in September 2018, a figure which has gone up significantly since then.

It's not claimed that his value is £3.6million, meaning that there's been an increase of £2.25million.

Given that he signed for around £7million this valuation is unlikely to go down well with supporters who are already skeptical over how much was spent.

The Middlesbrough player who has seen his value rise the second-most out of all of the squad.

Tavernier was a product of the club's famous youth academy which means that when he made his debut in August 2017 there was very little market value attached to him.

However since then he's really kicked on.

The advanced midfielder is now one of Middlesbrough's best attacking players and is said to be valued at £2.7million, meaning that his value has gone up significantly.

That said, any club who thinks that they'll be able to sign the player for that amount needs to think again.

The player who has seen his Middlesbrough value increase the most during his time at the club.

Fry is another player who came through the youth set-up at the club which means that he wasn't subject to a transfer fee when he arrived at the Riverside Stadium.

Since breaking into the first team the defender has really kicked on at both club level and with England under-21s.

It's said that Fry is now valued at £6.3million which means that he's Middlesbrough's most valuable player by some distance.

But once again, there's no chance that Middlesbrough would consider selling a player as important as Dael Fry for a fee such as that.