The Padres now have 38 players in Major League camp, including 32 from the 40-man roster and six non-roster invitees.
Luebke, a left-hander, tossed three scoreless innings in Saturday's 5-1 victory over the Dodgers. He walked three and struck out two. Luebke, who could always be used again during Cactus League play, has a 5.00 ERA.
Luebke will likely begin the season with Double-A San Antonio.
The three pitchers optioned to Portland all have Major League service time. Webb had an 18.00 ERA in four games this spring, while Perdomo (18.00) and Liz (8.22) also struggled at times.
"All three, with the exception of Luebke, have pitched in the big leagues and pitched well in the big leagues," Padres manager Bud Black said. "In these guys' case, the time isn't now."
Perdomo was 1-0 with a 4.80 ERA in 35 games for the Padres last season, working in mop-up duty. Webb, who was obtained in the July 5 deal with Oakland for outfielder Scott Hairston, was 2-1 with a 3.86 ERA in 28 games for San Diego after the trade.
Corey Brock is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.