Forwards Ade Yussuf and Evan Garnett and centre-half Jack Green have also been told that their futures lie away from the Pirelli Stadium.
Meanwhile, defender Andy Corbett will retire from football after his testimonial against Derby on Tuesday evening.
In Webster and Corbett, Albion are losing players with a combined total of 25 years' service to the club.
Webster is the Brewers' longest-serving player having only ever played for them since coming through the club's youth system in 1998.
Corbett joined Burton from Nuneaton Borough for a nominal fee in November 2003.