Montero worked in relief once with the Mets this season, on Aug. 22, but his last appearance out of the bullpen before that outing came in 2011, his first year in the New York organization after signing as a free agent in January. He has made 77 Minor League starts since then and six Major League starts this season.
Montero will also make a spot start against the Rockies at Citi Field on Wednesday.
"That was our plan all along," Collins said.
Montero, the Mets' No. 6 prospect according to MLB.com, was recalled from Triple-A Las Vegas on Friday night. He was 6-4 with a 3.45 ERA in 18 Minor League starts, striking out 87 in 86 innings this year. He was 0-3 with a 5.23 ERA in seven games (six starts) with the Mets.
"We love his arm," Collins said. "Everybody in this organization thinks he's going to be an outstanding Major League pitcher."
New York assigned jersey No. 50 to Montero, who is expected to arrive in Cincinnati sometime Saturday night.
Andy Call is a contributor to MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.