Middlesbrough captain Grant Leadbitter will miss the start of the Premier League season after undergoing surgery to repair a hernia problem.
The 30-year-old midfielder was a key figure in Boro's promotion drive last season despite playing through the final two months of the season only after having a series of painkilling injections.
Leadbitter has now had an operation, but the problem was more extensive than first thought and he will not now be fit for the start of the new season.
A statement on the club's official website, www.mfc.co.uk, said: "Grant Leadbitter is set to miss the start of the 2016/17 Premier League season after undergoing surgery earlier this year.
"The Boro skipper had an operation to correct an injury he had been carrying for the last two months of the season and further investigation has shown that the injury is worse than first anticipated."
Middlesbrough are hopeful of striking a deal which will bring Valencia forward Alvaro Negredo to the Riverside Stadium.
The newly-promoted Teessiders are understood to have opened talks over the 30-year-old former Manchester City frontman as head coach Aitor Karanka looks to boost the firepower at his disposal in the Barclays Premier League.
However, the negotiations are proving painstaking with Boro seeking an initial loan agreement without taking on full responsibility for the player's existing financial package.
Discussions are understood to have been ongoing for some time and, while progress has been made, any deal remains distant.
Madrid-born Negredo scored 23 goals in his one season at City before returning to Spain to join Valencia, initially on loan and then in a £19million permanent switch.
He has managed just five league goals in each of his last two LaLiga campaigns, although his physical presence has proved a major weapon.
Former Barcelona goalkeeper Victor Valdes has signed a two-year contract for newly promoted Premier League side Middlesbrough after his unhappy spell at Manchester United.
The club tweeted an image of Valdes alongside his new boss Aitor Karanka.
The 34-year-old spent part of last season on loan at Standard Liege after falling out of favour with former United boss Louis van Gaal.
Middlesbrough have announced Colombian defender Bernardo Espinosa is to be their second new signing of the summer.
The 26-year-old centre-half will join the promoted Premier League side on July 1 when his contract with Spanish club Sporting Gijon expires.
The Championship runners-up have already recruited Denmark winger Viktor Fischer from Ajax this summer.
Middlesbrough head coach Aitor Karanka is closing in on his first summer signing as he prepares for life in the Premier League.
Press Association Sport understands Ajax winger Viktor Fischer is due on Teesside to undergo a medical and discuss personal terms with the two clubs having reached agreement on a fee of around £3.8m.
Sources close to the player have indicated there is a four-year deal on the table for the Denmark international, who made 34 appearances for the Dutch club last season.
Karanka has wasted little time in starting to reshape his squad in the wake of promotion having released veteran Jonathan Woodgate and fellow defender Damia Abella at the end of their contracts on Tuesday.
It had already been confirmed that injury-plagued utility man Rhys Williams would be heading back to his native Australia to join Perth Glory.
Gareth Southgate has backed former club Middlesbrough to succeed in the Premier League after their promotion from the ChampionshipRead the full story ›
Middlesbrough are back in the Premier League after a 1-1 draw with Brighton was enough to clinch the second promotion placeRead the full story ›
Middlesbrough have been promoted to the Premier League after holding Brighton to a 1-1 draw at the Riverside StadiumRead the full story ›
Middlesbrough forward Cristhian Stuani has been charged for an "alleged act of violent conduct" by the Football Association.
An FA panel reviewed video footage of an incident during Saturday's 1-0 win over Preston which was missed by the match officials.
Middlesbrough have already confirmed they will appeal against the charge by the deadline of 6pm on Tuesday.
An FA statement read:
Cristian Stuani has been charged for an alleged act of violent conduct which was not seen by the match officials but caught on video. The Middlesbrough forward was involved in an incident in the 54th minute of their game with Preston North End on Saturday April 9, 2016.
The matter was referred to by a panel of three former elite referees who each reviewed the video footage independently of one another to determine whether they considered it a sending-off offence. For an FA charge to follow, the decision by the panel must be unanimous.
Middlesbrough head coach Aitor Karanka has resumed his duties at the Championship club.
There had been much speculation that the Spaniard would leave the Riverside after a failed attempt to smooth over a bust-up ahead of Sunday's 2-0 defeat at Charlton, which he missed.
But, in a statement on the club website on Monday evening, Boro said: "Middlesbrough Football Club can confirm that head coach Aitor Karanka will be resuming first-team duties with the club with immediate effect.
"We have 10 games left this season and as a club we are fully focussed on what remains of our Championship campaign."