The Phillies optioned him to Minor League camp Tuesday morning. They also reassigned right-handers Scott Elarton and Brian Sanches to Minor League camp.
Diekman threw five scoreless innings and held opponents to a .118 average in five Grapefruit League appearances, impressing Phillies coaches and front-office officials. Elarton, who is trying to make a comeback after not pitching in the big leagues since 2008, went 0-1 with a 5.02 ERA in 14 1/3 innings. Sanches had a 6.43 ERA in seven innings.
"I told [Diekman] he had a great spring," Phillies pitching coach Rich Dubee said. "I asked him first if he had an agent. He told me he did. I said, 'Fire him. Because I'll jump on and be your agent, and hopefully I'll be able to retire soon.' I think he's got tremendous upside. Seriously. That's what I told him. I expect to see him this year. If the call comes, I expect him to be ready."
Diekman went 0-1 with a 3.05 ERA in 53 appearances last season with Double-A Reading. He averaged 11.49 strikeouts per nine innings, holding left-handers to a .099 average. He also had a 0.79 ERA in 11 Arizona Fall League appearances.
Diekman, who the Phillies selected in the 30th round of the 2007 First-Year Player Draft, is likely to open the season in the Minor Leagues, but could see action at some point this season.
"I feel like I grew a lot down here," Diekman said. "I feel like I came a long way."