Chris Hughton has long been an admirer of the one-time Barcelona target, and tabled a £5million bid.
The 24-year-old is desperate for a shot at the Premier League and earlier this summer hit out at United's chairman Ken Bates.
The former Livingston player was offered improved terms to remain at the Yorkshire club, but was not willing to sign.
He said: 'I'd love to get into the Premier League with Leeds. I'm captain now which is a different challenge. The chairman is trying to put a bit of pressure on me and he's telling me what plans he has for the club.
'But they told me the same type of plans the season before and it didn’t work out so it's hard to buy into these things again.'