CALGARY — Calgary Stampeders quarterback Bo Levi Mitchell has been placed on the 6-game injured list, the team revealed Friday.

Backup pivot Nick Arbuckle will get the start on Saturday when the Stamps take on the Saskatchewan Roughriders at Mosaic Stadium in Week 4.

Mitchell suffered an upper body injury in Week 3 and underwent an MRI on Tuesday, but the team was reportedly seeking a second opinion on the results, TSN’s Farhan Lalji reported.

The reigning Most Outstanding Player left the game against BC with what initially looked like shoulder discomfort late in a 36-32 win over the Lions on Saturday. However, he said after the game in an interview that his shoulder wasn’t affected, instead indicating it was his pectoral muscle.

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Arbuckle, a 25-year-old sophomore, was spectacular in relief last weekend, completing all nine attempts and finding the end zone twice to lead an impressive last-minute comeback.

Despite a slow start this season — averaging just 7.2 yards per attempt with three touchdowns and two interceptions — Mitchell is considered one of the best quarterbacks in the CFL. The two-time Grey Cup Champion and Most Outstanding Player signed a four-year contract extension in the off-season.

Injuries continue to mount for the Stamps, who were also affected by a number of key departures in the off-season.

Running back Don Jackson and receiver Hergy Mayala were also added to the six-game injured list, while receiver Juwan Brescacin will miss at least Saturday’s game after leaving the second half of Week 3’s matchup.

Kadeem Carey has been activated from the practice roster and could pick up some of the slack at running back along with Terry Williams.