Wycombe Wanderers say they have "reluctantly agreed" to sell Luke O’Nien to Sunderland for an undisclosed fee.
O’Nien will leave Adams Park after three years, subject to the transfer being finalised over the weekend.
Sunderland are also close to confirming the signing of Jack Baldwin from Peterborough United for a fee believed to be worth £200,000 as Jack Ross' summer rebuild steps up a notch.
O’Nien is a box-to-box midfielder and will add another dimension to Sunderland's midfield options.
With his contract due to expire next summer, Wycome say they have taken the decision to allow the 23-year-old to pursue his career at the Stadium of Light.
Wycombe Chairman Trevor Stroud said: “This is one of the toughest decisions we’ve had to make as a football club board in recent times, but ultimately the sustainability of the club under supporter ownership is our number one priority and the reality of our situation is that we need to rely on football fortune – player sales and cup runs – to achieve our breakeven model.
"As Chairman, with the board’s support, I had to make the decision for the club and it needs to be said this would not have been the manager’s choice from a footballing perspective.
“Luke has been a fantastic ambassador for the club on and off the field and we’re sorry to see him go, but he has an exciting adventure ahead of him at undoubtedly the biggest club in League 1 and we wish him all the best for the future.”
Sporting director Andrew Howard added: “Luke is yet another success story for the club under Gareth’s management and we should all be immensely proud to see another excellent young talent move on to bigger things.
"We have to remember that he was a young kid who’d been playing on loan in non-league before he came here, but his attitude has always been first-class and his hunger to learn and improve obvious to everyone.
“Whilst we have worked to try and keep Luke, a club our side will always struggle to keep players against the bigger clubs. He will be a loss to us, and we hope he achieves great things in his career, but now we will turn our attentions to helping Gareth continue to build a squad capable of achieving our aims this season.”
The midfielder made 119 appearances for the Chairboys, scoring 16 times and becoming an integral part of the club’s journey towards winning promotion to League 1.