Janssen is expected to miss the first two weeks, a damaging blow to the veteran right-hander after he made a quick recovery from a shoulder injury earlier in the spring, only to be let down in the end by his back.
"I wanted, obviously, to pitch," Janssen said. "It's probably not the smartest thing to do and I don't know how it would react if I were to throw on it tonight. If I got that same feeling that I had on Friday, I'd be worthless for a couple of days.
"Unfortunately, it's probably the smart move, but I hate going on the DL. I want to go out there and compete and help my team, and you can't do a whole heck of a lot when you're on the DL."
Janssen had been limited to just three official spring appearances because of a sore shoulder. There were some initial concerns about whether he would be ready to start the season, but as camp neared a close, everything looked like it was going to be fine.
The 32-year-old had said in those finals days that his arm and shoulder were feeling great, a lot better than they did just one year ago after he experienced similar issues. The only road block Janssen had to clear was pitching against the Mets in Montreal on Friday night in his final scheduled outing.
The back problems began while warming up in the bullpen for that appearance. He felt some tightness in his lower back/left abdominal area, and even though it wasn't enough to stop him from pitching, the discomfort stuck around for the next two days and prompted the club to have Janssen undergo an MRI.
The results revealed a minor strain and Janssen has been ordered to stop throwing until the tightness subsides. Janssen's goal is to be ready when his 15-day DL stint ends April 13 in Baltimore, but there is a danger of having that timeline pushed back unless he's able to resume throwing relatively quickly.
"I don't know, I'm chomping to get going," Janssen said. "I know just a little bit of rest will hopefully calm this thing down enough to where I can keep my arm in shape. As long as I don't lose that, I think it will be quick."
During Janssen's absence, the Blue Jays will hand the closing duties over to Sergio Santos, who recorded 30 saves for the White Sox in 2011. Santos was originally acquired to become Toronto's primary closer following that season, but he eventually lost the job because of prolonged injuries.
Santos is expected to receive most of the save opportunities but manager John Gibbons also didn't want to completely rule out the possibility of using others such as Steve Delabar or Brett Cecil, depending on the situation.