Cubs DFA former closer Jose Veras

CHICAGO -- The Cubs designated Opening Day closer Jose Veras for assignment and placed catcher Welington Castillo on the disabled list with a left rib cage injury, the club announced on Tuesday.

"You're disappointed whenever you sign a free agent, bring in a veteran and it didn't work out," general manager Jed Hoyer said before the Cubs played the New York Mets Tuesday night.

The Cubs signed Veras to a $4 million contract with a $5.5 million option for 2015 in the offseason to give them a veteran option at closer. Despite a shaky spring, Veras won the job for the start of the season, but the struggles continued with two blown saves in his first four appearances. His ERA was 8.10 when he was demoted on Tuesday.

"There is nothing more volatile than a reliever," Hoyer said. "I hope for his sake because he's a great guy and a great mentor he gets back on track."

Hoyer said he's also hopeful some teams are interested in trading for Veras as he's produced a 2.35 ERA since coming off the disabled list with an oblique strain. Reliever Hector Rondon was activated off the paternity list to take his place on the roster. Rondon is also the Cubs closer now.

Castillo said he felt something in his rib cage in his first at-bat on Sunday in Milwaukee. He came out of the game and believes two weeks should get him healthy.

"I took a swing and felt something (there)," Castillo said. "I thought I could keep playing but it got worse and worse.

Veteran Eli Whiteside was called up from Triple-A Iowa to take Castillo's place.