The 27-year-old centre-back is out of contract at Huish Park after making 98 appearances during a two-year stay and Lions boss Holloway has explained what he believes Webster will add to his squad.
"I think he will improve our squad's strength," Holloway told the Southwark News. "We're trying to improve the goals against column, so to do that you've got to stop goals going in.
"I like how Byron uses the ball from defence and I think he can play left or right side, and with him I can also change my tactics and go three at the back if I need to.
"Hopefully someone like Byron can step up to the plate for us. I think he's in our bracket of the right age and wants to improve his career having just had one season in the Championship."