The Clarets will receive £100,000 for Foster, the second defender sale in the last week to earn the Turf Moor club a profit.
Foster has spent just over a year in Lancashire, signing from Crewe in the summer of 2006, but his first team chances have been limited.
His last Burnley appearance was in the Carling Cup tie last week at Grimsby when he played the entire 120 minutes at right-back.