Middlesbrough have accepted a £13m bid from Serie A club Atalanta for midfielder Marten de Roon.
The 26-year-old Dutchman joined Boro from the Italian side last summer in a £12million move ahead of their return to the Premier League, but has been linked with a return this summer.
It is understood the Teessiders have now agreed a fee of £13million to allow De Roon, who started last Saturday's 1-0 Sky Bet Championship defeat at Wolves, to head back to Italy.
Boro have spent heavily during the summer window with £15million striker Britt Assombalonga heading a list of incomers which also includes Darren Randolph, Ashley Fletcher, Martin Braithwaite, Cyrus Christie and Jonny Howson.
They have recouped in the region of £10million for Gaston Ramirez following his move to Sampdoria, while Viktor Fischer, Cristhian Stuani, Brad Guzan, James Husband and Alex Baptiste have also left the Riverside Stadium, and a successful conclusion to the De Roon deal would help to balance the books.
Middlesbrough are 2/1 favourites at Sky Bet to be promoted this season and are also 13/2 favourites to win the title.
There is also interest in England defender Ben Gibson with West Brom having shown their hand, although manager Garry Monk has repeatedly stressed that Boro are under no pressure to sell their prize asset.
Gibson, who is 3/1 to join Premier League side West Brom on Sky Bet, is also 10/11 to stay at Boro as they attempt to regain promotion to the top flight.
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