Outfielder Gabby Guerrero and right-handers Jake Barrett and Matt Koch were placed on the roster Friday.
Koch, acquired in an August trade with the New York Mets, went 5-8 with a 3.20 ERA with Double-A Binghamton and Mobile last season.
Barrett was 4-3 with a 4.58 ERA with Mobile and Triple-A Reno.
Webster went 1-1 with a 5.81 ERA in nine games during his only season with Arizona. He spent the previous two seasons with Boston.