With the Fishercats, Loup went 0-3 with three saves and a 2.78 ERA in 37 relief appearances. In 43 1/3 innings, Loup, a ninth-round pick in the 2009 First-Year Player Draft, walked 14, while striking out 43.
He will join the club for Friday's series opener against the Indians at Rogers Centre.
"Someone who has really come on, someone the New Hampshire staff likes quite a bit," general manager Alex Anthopoulos said. "I think we should give him a shot and see what he can do for us."
Manager John Farrell said he saw Loup in Spring Training, and said the biggest thing he noticed was that Loup is effective in getting hitters out. The decision to turn to him was based on the need to have another lefty in the bullpen.
Farrell said Loup has a true three-quarter arm slot and that he can "sweep a breaking ball away from a left-hander," while describing his delivery as a little bit deceptive.
"By all accounts that have gone through New Hampshire, and have seen him, particularly over the last six weeks or so, he has grabbed the attention of everyone, Farrell said. "With the unfortunate situation with Luis, once again opportunity knocks, and Aaron is here to step up and take advantage of it."
Perez, who has a UCL tear in his left elbow, is scheduled to visit Dr. James Andrews this weekend and is expected to undergo Tommy John surgery, according to Anthopoulos.
The 27-year-old Perez joins pitchers Kyle Drabek, who underwent his second Tommy John surgery, and Brandon Morrow (oblique) and Drew Hutchison (elbow) on the disabled list.
Toronto has been forced to turn to Minor League pitchers all season, many of whom have little to no Major League experience. Farrell said the pro environment can cause pitchers to become inconsistent, but he stressed the importance of not leaning on trusted relievers Jason Frasor, Darren Oliver, Casey Janssen too much.