The Padres designated Ambriz for assignment because the rules -- optional assignment waivers -- prohibit them from optioning him back to Triple-A El Paso.
If the right-hander clears waivers, the Padres hope to retain Ambriz, who had a 1.62 ERA in 14 games for El Paso.
This is Quackenbush's second stint with the Padres, and it figures to be longer than his first -- one game. The Padres added Quackenbush to the roster on April 25. He allowed two runs in 1 2/3 innings in his lone appearance that day and was optioned back to El Paso two days later.
In the interim, Quackenbush tossed 4 1/3 scoreless innings for El Paso. Overall this season, his ERA is 1.26 in 13 games for the Chihuahuas.
There will be another roster move coming Saturday when the Padres are expected to activate Chase Headley from the disabled list. Outfielder Carlos Quentin won't likely be too far behind Headley, which means the Padres have two moves to make in the coming days.
Corey Brock is a reporter for MLB.com. Keep track of @FollowThePadres on Twitter. This story was not subject to the approval of Major League Baseball or its clubs.