Roenicke, 32, has pitched in 190 Major League games over six seasons, most recently appearing in 63 games for the Twins in 2013. Last season, he posted a 6.04 ERA in 29 games for Triple-A affiliates of the Rockies and Nationals.
He has extensive family ties to the Major Leagues. His father is former Orioles outfielder Gary Roenicke, and his uncle Ron Roenicke has managed the Brewers since 2011. Josh Roenicke is also the brother-in-law of Nationals infielder Ian Desmond since marrying Desmond's sister in 2010.
Herndon, 29, pitched in 97 games for the Phillies from 2010-12 with a 3.85 ERA, but he hasn't made it back to the Majors since undergoing Tommy John surgery in 2012. Herndon would make the Major League minimum salary should he earn a callup, and he has two Minor League options remaining.
"I'm 100 percent for the first time since 2011," he said by telephone from his Florida home. "I'm really excited for this season."
He missed most of 2012 and part of '13 because of the elbow injury, then saw his comeback derailed by a freak accident two days before his December 2013 wedding. Herndon required surgery after slicing the index finger on his pitching hand while trying to modify a baseball to carry his and his bride's wedding rings. When he tried to ramp up quickly in February, he suffered a shoulder strain that essentially ruined his 2014 season. Herndon pitched only five times for the Yankees' Triple-A club.
A two-seam fastball specialist, Herndon was encouraged this week when he worked at 90-92 mph during a 15-pitch tryout with the Padres.
"That gave me the encouragement I needed," he said. "It confirmed what I already knew about being back to 100 percent."
Adam McCalvy is a reporter for MLB.com. Read his blog, Brew Beat, and follow him on Twitter at @AdamMcCalvy. This story was not subject to the approval of Major League Baseball or its clubs.