The team's fear that Mendez might miss the entire year was allayed Monday when an MRI revealed the 24-year-old lefty has a Grade 1 sprain of the ulnar collateral ligament.
"It's really good news. I think we dodged a bullet," assistant general manager Shiraz Rehman said. "There's some inflammation and some fluid in there, but no surgery at all. At this point, six weeks of no throw, and then we'll build him back up."
That timetable calls for an April 29 return to throwing, beginning on flat ground from a close distance. By the time Mendez is ready to pitch in a game, it is likely to be another six weeks, probably in mid-June.
"Think of him as a second-half pitcher for us at this point, because we want to be conservative with it," Rehman said.
Mendez left Sunday's Cactus League game against the Diamondbacks after striking out the first batter he faced in the third inning.
"It hurt on that last pitch," he said. "I felt something in my elbow. It felt weird. I said, 'No more.'"
The Rangers have three projected starters, Shelby Miller, Drew Smyly and Edinson Volquez, returning from Tommy John surgery, so Mendez was expected to provide depth in the early part of the season. While that is no longer the case, he could play a role if needs arise in the second half.
"With the depth that guy provides us, it's huge," manager Chris Woodward said. "He had a really good spring training. He was really committed to how he was throwing his pitches, where he was throwing, so to not have to lose him for an entire year is really big for us."
The Venezuelan native and former prime prospect went 2-2 with a 5.53 ERA in eight games, five starts, for the Rangers last year. He has appeared in the majors each of the past three seasons.
"It is good news because I am not going to miss the whole year," Mendez said. "I am going to prepare and stay healthy until I can return."