The 32-year-old right-hander has been dealing with a strain in his lower back and abdominal muscle. He was officially placed on the disabled list March 30 but has been essentially hampered by the injury since spring training.
Manager John Gibbon said Janssen is going to throw a bullpen session "very soon."
"He's feeling better but something is still nagging him a little bit," Gibbons said before Friday night's game against the Boston Red Sox.
Janssen will likely throw at least two bullpen sessions before another rehab assignment in the minors.
"I don't see him back here in the next couple of weeks, to be honest with you," said Gibbons.
The manager said while there has been no physical setback, Janssen is still not feeling 100 per cent.
"There's still something there that's holding him back a little bit," Gibbons said. "Psychologically he doesn't feel quite ready to cut loose because something is just nagging at him there, in his oblique."
Janssen has seen action in just three games this season, working three innings with a 3.00 earned-run average.
The hard-throwing reliever has already had one rehab assignment in the minors cut short after being told to take more time off.
Sergio Santos has been operating as the Jays' closer in Janssen's absence, converting five-of-six save opportunities heading into play Friday.
NOTES — First baseman Adam Lind is making progress with his lower-back tightness. Gibbons said Lind, who is on the disabled list, had started swinging the bat ... Gibbons also said the club is having Chad Jenkins operate as a reliever at triple-A Buffalo because that's where it believes he can best serve the major league club ... Reliever Aaron Loup has been dealing with a bug that has laid him low.