Coello was promoted from Triple-A Las Vegas on Thursday to provide more depth in the bullpen. The 27-year-old was involved in one of five corresponding roster moves made by the Blue Jays in the past week, while the club made a total of seven during May.
"He'll provide another arm in the bullpen for us," Blue Jays manager John Farrell said. "Even though he came off his last outing in five innings, he has the ability to go multiple innings if the game situation arose or how this series goes. He provides us with some additional insurance."
Coello posted a 3-1 record with a 3.22 ERA in 17 games this season for Las Vegas. He has appeared in just six games at the Major League level while posting a 4.76 ERA.
Farrell was his pitching coach in Boston during the 2010 season and said Coello's development of a fork ball has made him a more effective pitcher since that brief stint with the Red Sox.
"He's got some swing and miss to his fastball," Farrell said. "Having worked with him, four years ago, his breaking ball has tightened up a little bit more. I think he has a rare and somewhat unorthodox fork ball that is more of a true tumbling-type fork ball as opposed to a split-finger. It's a pitch you rarely see at any level in pro baseball."
The Blue Jays currently have eight relievers on their 25-man roster. They are expected to go back to seven following a three-game series against Boston as Farrell would like to add another position player into the mix.