Barnsley head coach Paul Heckingbottom admits they face a battle to keep hold of Alfie Mawson.
Sunderland are among clubs keen on the defender.
The Sunderland Echo says a host of Premier League and Championship clubs tracking the former Brentford player, 22.
Heckingbottom, the ex-Sunderland defender, said “interest is growing" in the defender.