PHOENIX -- The Arizona Diamondbacks have added three prospects to their 40-man roster and designated right-hander Allen Webster for assignment.
Outfielder Gabby Guerrero and right-handers Jake Barrett and Matt Koch were placed on the roster Friday.
Guerrero was acquired in a June trade with Seattle that included outfielder Mark Trumbo and left-hander Vidal Nuno. Guerrero is playing in the Arizona Fall League for top prospects.
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.