Middlesbrough are reviewing their transfer business while Garry Monk was manager, amid the club's concern about his relationship with his agent James Featherstone.

On Wednesday, Birmingham City's chief executive Xuandong Ren claimed Monk was fired this week after a dispute over the use of his own agent, Featherstone, in many of the club's transfer deals.

Sportsmail can reveal that Boro are also examining the deals that were done at the Riverside during Monk's brief tenure.

Middlesbrough are reviewing their transfer business while Garry Monk was manager

Monk was dismissed by Birmingham this week due to a dispute, according to the club's CEO, regarding the use of Monk's agent James Featherstone (R), in the club's transfers

They say they made it clear to Monk when he was manager they did not want Featherstone involved in club transfer business.

While there is no suggestion of any wrongdoing by Monk or Featherstone, a senior Boro insider has said their relationship was one of the key reasons behind the former Swansea boss's sacking in December 2017.

Monk survived only six months as Boro manager after joining the club in June of that year but still spent around £50million on players in the summer transfer window.

At the time, Boro chairman Steve Gibson said it was with 'a heavy heart' that he was dismissing the then 38-year-old, having expected him to make a more immediate impact. Monk signed 15 players during his six months in charge of the club, including a club record £15million on Nottingham Forest striker Britt Assombalonga.

Xuandong Ren claimed his relationship disintegrated with Monk when he told the Blues boss he could no longer use his agent James Featherstone in 'all' the club's transfer deals

Other significant deals included a £9m move for Toulouse forward Martin Braithwaite and £6.5m for West Ham striker Ashley Fletcher. According to published FA data, Featherstone was directly involved only in the deal to bring Cyrus Christie from Derby County to the Riverside in July 2017 — although that was as a representative for the selling club.

Acrimony followed Monk's departure from the North East. As Birmingham chief executive Ren hinted, there was a legal dispute between Boro and Monk over his contractual entitlement. By April 2018, it emerged that Boro were suing Monk's backroom team, as well as Birmingham City after they employed the group at St Andrew's.

A legal first in football, Middlesbrough claimed Birmingham were given a competitive advantage by employing Monk's coaching staff. They had been placed on gardening leave when Monk was sacked, but quit in the March to join their manager at Birmingham.

There was reportedly a clause in their contracts that prevented them from working together or alongside Monk for a Championship rival until the end of the year. Boro sought damages and the removal of the Birmingham backroom team until the end of the year. It is understood the two parties reached a settlement.

Garry Monk spent £50million during his tenure on Teesside between June and December 2017

As Ren told Sportsmail this week, their relationship disintegrated when Monk was told he could not use Featherstone in all the club's transfer deals. According to data published earlier this year by the FA, Featherstone was involved in nine of the 18 deals conducted by Birmingham after Monk arrived at the club in March 2018.

Ren said: 'I said "Look I've got the football club to look after and if you let one agent control all transfers it's very dangerous". I think the fall-out started from there.'

On Thursday Monk issued a statement via the League Managers' Association, saying: 'I am aware of certain disappointing comments the club has made in the wake of my dismissal.'

Featherstone told Sportsmail: 'The club were always and still are fully aware of all transfer activity, therefore I am confident of the outcome of any investigation.'