"I'll tell everybody ahead of time, this is going to be tough," manager Jim Leyland said. "It'l be a second-guesser's delight, a second-guesser's heaven."
Luis Marte also was optioned to Toledo, leaving the Tigers with seven relievers and five starting pitchers on their active roster ahead of Monday's opener at Minnesota.
Jose Valverde struggled in the postseason last year and became a free agent, and the Tigers brought the 22-year-old Rondon to camp as his potential replacement.
"Any one of them can close the game," Leyland said. "Any one of them might get the ball to get the third out in the ninth. That's pretty much the way you have to do it when you're in this situation, which is fine. Look for anything because that's the way it's going to be."
Rondon went 2-1 with a 5.84 ERA in 13 spring training games with nine walks and 19 strikeouts in 12 1-3 innings.
His velocity was clocked at as high as 101 mph, and he tried to mix in more breaking pitches later in spring training.
"A lot of times in the minor leagues, when you throw that hard, you don't need those other pitches to get outs," catcher Alex Avila said. "It's just a learning curve, being able to learn when to use your other pitches, learning how to pitch rather than throw. But he's as close as you can get without being ready to make an impact. I wouldn't be surprised if he makes an impact this year with is at some point."
Valverde saved 110 games for the Tigers over the last three seasons and led the AL with 49 in 2011.
Rondon, a Venezuelan who signed as a 16-year-old, has pitched only eight innings at Triple-A.
"My wish is for him to master his two-seamer, his four-seamer and his slider," Leyland said. "I don't think he needs to master the changeup; I think that's too much for a kid. Right now, for development purposes, just put the changeup on the back burner and get the command of the fastball and the breaking ball."
Leyland stressed that Toledo is just an hour away and that Rondon could join the big league roster at some point.
"The kid did not do one thing wrong," Leyland said. "What we evaluated was that he wasn't quite ready to do it today or April 1 here."