The England Under-21 ace has emerged as one of the most sought-after young defenders outside the Premier League.
The 22-year-old is a graduate of Leeds' highly acclaimed academy, and has already chalked up over 50 appearances for the club.
Lees is now attracting interest from a number of clubs, who have been impressed with his consistent displays at the heart of Leeds' promotion-pushing defence.
Celtic have been keeping close tabs on Lees for some time, but there is also interest from the Premier League and Championship too.
Aston Villa, Queens Park Rangers, Wigan and Cardiff are all thought to be monitoring his situation.