The club have also confirmed that Husband and Ayala are set to be sidelined.
Leadbitter is set to miss the start of the new season
Middlesbrough captain Grant Leadbitter will miss the start of the new Premier League season with a hernia problem, with the club's official website also confirming that James Husband and Daniel Ayala are set for lengthy spells on the sidelines.
The 30-year-old played through the pain barrier during the last two months of the season before having an operation earlier in the summer, with the extent of the problem found to be worse than previously anticipated.
The midfielder was a key part of Middlesbrough's promotion push last term
It means the midfielder is now set to miss the start of Middlesbrough's first Premier League season in eight years.
Leadbitter played a significant role in helping his team achieve promotion to the top flight and his potential absence will come as huge blow for boss Aitor Karanka.
The news will come as huge blow to Boro boss Karanka
A statement on the club's official website read: "Grant Leadbitter is set to miss the start of the 2016/17 Premier League season after undergoing surgery earlier this year.
Middlesbrough are preparing for their first Premier League season in eight years
"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."
Meanwhile, full-back Husband could be sidelined for three months after dislocating his shoulder during Saturday's 6-0 pre-season friendly win over York City, while central defender Daniel Ayala will sit out this weekend's friendly trip to Doncaster due to an ankle problem picked up in training.