The 6-foot-5, 230-pound left-hander entered Spring Training as the Nationals' No. 4 prospect (86th overall). He features a plus changeup, a very good breaking ball and outstanding command of a fastball that has picked up velocity since his professional debut.
"He is a terrific prospect," Rizzo told MLB.com. "He has great stuff. We always thought, even after we drafted him, he was quick to the big leagues. This [the surgery] will derail that a little bit."
A second-round pick out of the University of San Diego in 2010, the 23-year-old Solis has struggled with injuries in his brief pro career. A groin issue pushed back his 2011 debut until May 30 and elbow problems cut short his Arizona Fall League campaign in November.
Solis, who had been instructed to rest his arm after tests in November proved inconclusive, only resumed throwing after reporting to Nationals camp in Viera, Fla., last week. He traveled to California on Sunday, where specialist Dr. Lewis Yocum confirmed that Solis needed surgery.
"He passed all of the tests ... as far as the physical part of it," Rizzo said. "Because he passed all of the physical tests that they put him through, they felt the most prudent course of action would be to have him rest for a month then ramp him back up into a throwing program to see if we could avoid the Tommy John surgery."
Yocum, the Angels' team physician, performed elbow ligament surgery on Nationals pitchers Jordan Zimmermann in 2009 and Stephen Strasburg in 2010. He is a protégé of Dr. Frank Jobe, who pioneered the surgical technique on Tommy John in 1974.
Solis compiled an impressive 8-3 mark with a 3.26 ERA in 17 outings for Class A Hagerstown and Class A Advanced Potomac in 2011. He was also named the AFL's Pitcher of the Week for the first week of November after striking out nine over four scoreless innings.