Nottingham Forest has rejected an offer of £ 30.2 million for Strasbourg winger Dilane Bakwa.
Four Premier League clubs have asked questions for the 22-year-old, including Leeds United, but Forest has pushed the most difficult for the French U21 International.
Strasbourg, however, retains £ 35 million plus add-ons for Bakwa that has also attracted interest from Sunderland.
The conversations go on while Bos tries to bridge the last gap in negotiations prior to their rivals.
In the meantime, Leeds United has confirmed the signing of full-back James Justin from Leicester City with a four-year deal.
Daily Mail Sport reported on the weekend that a package consisting of an initial £ 8 million that could rise to £ 10 million in potential add-ons.
Justin, 27, started and captain Leicester in their opening of two champion matches, but was omitted from the team for Saturday's 1-0 win at Charlton Athletic after picking up a dead leg. He also asked Everton questions.