Francis gave up three runs over five innings of work in his start, taking the loss.
Playing for Triple-A Louisville this season, Francis struck out 45 and walked 12 in 48 2/3 innings over eight starts.
Oakland manager Bob Melvin likes the options that Francis presents.
"We'll bring him in here," Melvin said. "Mostly length at this point, [but Francis is] a guy that's stretched out to start and helps us out two different ways -- [as] potential starting depth and the true long man we need back into the bullpen, too."
Oakland moved Jake Elmore to the 60-day disabled list to make room on the 40-man roster for Francis. Francis will join the team on Monday in St. Petersburg in advance of Tuesday's series opener against the Rays.
Francis was added to the 25-man roster when pitcher Joe Savery was optioned to Triple-A Sacramento.