Sunderland have accepted Middlesbrough's bid in excess of £5m for midfielder Paddy McNair, according to Sky sources.
The 23-year-old former Manchester United youth has also been a target for Premier League Brighton, who have seen two bids turned down - the second of those £3.5m.
And it remains unclear whether Brighton intend to make another offer for the player after Boro's proposal was accepted.
Sunderland, who were relegated to League One last season, are also understood to have turned down an offer of £3.75m for McNair from an unnamed London-based side.
The Northern Ireland international impressed last term despite the Black Cat's plight, making 18 appearances and scoring five goals.
He made several first-team appearances for United in 2014 before joining Sunderland in August 2016.
Tony Pulis led Middlesbrough to the Championship play-offs last season but they lost 1-0 on aggregate to Aston Villa in the semi-finals and intend to rebuild for another promotion-push next term.