Walden will officially take the spot of right-hander Jeremy Jeffress, who was designated for assignment following the Blue Jays' 7-2 loss to the Yankees on Friday night.
"You can't bring a guy on the [40-man roster] back for 10 days unless there's an injury," general manager Alex Anthopoulos said. "They have to be on option for 10 days. So guys like [Neil] Wagner, anybody on the 40 -- [Mickey] Storey, [Sean] Nolin, the list goes on and on. They have to be on option for 10 days in the season unless somebody gets hurt."
The 25-year-old Walden is exempt from that rule because he wasn't on the 40-man roster and didn't need to be optioned to the Minor Leagues at the end of Spring Training. He made one appearance for Triple-A Buffalo this season and allowed just one hit in one inning.
Walden, taken in the ninth round of the 2007 First-Year Player Draft, spent last season with Double-A New Hampshire and went 6-14 with a 3.71 ERA in 26 starts. With his background as a starter, he has the ability to throw multiple innings, and that's especially valuable considering the Blue Jays' bullpen pitched 6 1/3 innings on Friday night.
"He has a good arm, he's a strike-thrower, he can get some ground balls," manager John Gibbons said. "I had never seen him before. The organization has always liked him, and he impressed me during Spring Training. He can throw some innings for you, he's used to starting.
"He can throw strikes; that's the key. You have a chance when you throw strikes. If you don't, it makes it tough, and you're killing the guys playing behind you."
Though Jenkins' promotion has been delayed for the time being -- he will be eligible on April 10 -- it's very possible it won't be long before he eventually gets that call again. Gibbons is a big fan of what Jenkins did last season and during Spring Training.
"I had been pounding and pounding to get him up here from the day we sent him down, but he's not here," Gibbons said of the 26-year-old Jenkins, who posted a 2.70 ERA in 33 1/3 innings last season.
Gregor Chisholm is a reporter for MLB.com. Read his blog, North of the Border, and follow him on Twitter @gregorMLB. Jamie Ross is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.