TORONTO – Brett Cecil is likely to miss at least a month with a tear in his lat muscle discovered during an MRI earlier this week, another blow for the already beleaguered Toronto Blue Jays bullpen.

Cecil, the club’s primary left-handed reliever expected to be a key set-up man for closer Roberto Osuna, went on the disabled list Sunday with what the club described at the time as triceps tightness.

He had an MRI on Monday at the club’s facilities in Dunedin, Fla., where the injury to his lat, or latissimus dorsi muscle, was found. The lat runs from the lower back through to the armpits and the upper arm.

The injury is similar to the one that kept Aaron Sanchez out of action from June 15-July 24 last season. At first, the club planned to build Sanchez back up as a starter before switching him into a relief role, a process that initially led to an extended rehab assignment.

Cecil is 0-5 with a 5.23 earned-run average in 16 games so far this season and expressed a belief Sunday that the injury wasn’t a serious one, describing the MRI as something “just for peace of mind and precautionary reasons.”

He said that day he first felt “a tug” in his arm while throwing warmup pitches on the mound May 3 in Toronto, and didn’t pitch again until Saturday after returning from a paternity leave. The thinking was that the extra rest would make the issue go away, but while he warmed on the mound at Globe Life Park, he felt the tug again and pitched through it as best as he could.

Chad Girodo and switch-pitcher Pat Venditte are currently the only left-handed relievers on the roster with Cecil joining Franklin Morales and Aaron Loup on the disabled list.

Morales, out with shoulder fatigue, had his $2-million, one-year deal become guaranteed Wednesday after he spent 45 days on the roster. He continues to build up arm-strength and there’s no timeline yet for him to get back up on a mound.

Loup (forearm) threw two-thirds of an inning Tuesday in his second rehab outing for single-A Dunedin, allowing two walks with a strikeout.