Turner, 21, already has topped his innings total from 2011. The club is being careful with the right-hander, who will now get the start on Friday at Washington.
"LeBlanc is going to start," manager Ozzie Guillen said. "Just because we're worried about Turner's innings. We're going to give him a little rest. He's never pitched in September. He never pitched that many innings."
Turner has thrown 23 1/3 innings at the big league level, and 111 2/3 innings in the Minor Leagues, giving him 135 total this season. A year ago, he compiled 143 2/3 innings, with 12 2/3 coming with the Detroit Tigers.
The Marlins acquired Turner from the Tigers on July 23 as part of the Anibal Sanchez/Omar Infante trade.
"Obviously, your body is getting tired," said Turner, who has made two starts with Miami. "If you condition the right way throughout the season, I think you're prepared for it."
Miami opened a four-game set with Milwaukee on Monday. After LeBlanc throws on Tuesday, Nathan Eovaldi will start on Wednesday, and Josh Johnson will close out the series on Thursday.
Turner will get the nod in the first game at Washington on Friday. Mark Buehrle will start on Saturday, and Ricky Nolasco will go on Sunday.
The revised rotation means Johnson, Nolasco and Buehrle will each have one fewer start.
"I don't want to burn any bullets when the guys don't need to," Guillen said. "They're only going to miss one start, the big boys. It gives us an opportunity to rest those guys, and see those kids."
Buehrle has a string of 11 straight seasons with at least 200 innings. The veteran lefty is at 173 2/3 innings. So if he averages seven innings in his final four starts, he would finish up with 201 2/3 innings.