The Blue Jays selected Dallas' contract from Triple-A Buffalo on Thursday.
Dallas is in line to serve as the bulk reliever Thursday in Atlanta in what will be his major-league debut. The 25-year-old has put up a 4.50 ERA and 38:13 K:BB over 36 innings during his time with Buffalo this season in his first year back from Tommy John surgery. Dylan Cease (hamstring) and Max Scherzer (forearm) are both due back soon, so Dallas could be sent back down following Thursday's outing.