Kevin Glenn will start for the Stampeders in Sunday's West final in Vancouver versus the B.C. Lions.
Tate was sidelined 14 of 18 regular-season games because of a shoulder dislocation.
In just his third game back, Tate fractured a bone in his throwing arm during the third quarter of Sunday's division semifinal versus the Saskatchewan Roughriders.
The 28-year-old finished the game and threw a 68-yard touchdown pass to Romby Bryant with 20 seconds to go for a 36-30 win. But Tate says he felt pain in his arm prior to that drive.
Tests confirmed a broken bone in his lower right arm.
"I guess 2012 just wasn't my year," Tate said following Thursday's practice at McMahon Stadium.
"One door closes. Another opens and the opportunity is now Kevin's. Kevin will take advantage of it and I think our team will respond."
Glenn went 9-5 when Tate was sidelined during the season.
"We won 10 out of the last 12. Kevin started eight of those wins so we'll just move on," Stampeders coach and general manager John Hufnagel said.
It's been one thing after another for the Stampeders this week.
Tate's head and not his arm was the issue after Sunday's game.
When the quarterback said during post-game interviews that he couldn't remember the first half, that sparked fears he'd suffered a concussion.
The quarterback issued a statement the following day saying he'd been misunderstood.
Just as that fire was getting put out, Calgary receiver Nik Lewis posted this questionable tweet on his Twitter account:
"I just bought OJ's gloves on eBay. Now all I need is a white girl named Nicole." He added the hashtag #MaybeALittleToFar.
The reference was to the 1995 murder trial of former NFL player O.J. Simpson, who was asked in the courtroom to put on leather gloves found at the crime scene.
Lewis's semi-sincere apology Wednesday obviously wasn't enough for the Stampeder ownership group, which is the NHL's Calgary Flames.
He was much more contrite in both a printed and verbal statement Thursday.
"I never would condone violence to anyone, especially women," Lewis said after practice. "I made a mistake by making that comment on Twitter and I take full responsibility for that comment.
"I would like people to know I am a better person than that."
Lewis will donate his paycheque from Sunday's game to the women's emergency shelter in Calgary and the team will match the amount with another donation.
Back to the quarterback plot, an X-ray on Tate's arm earlier this week didn't show cause for alarm, but he didn't take any snaps Wednesday.
Hufnagel had expected Tate to participate in full practice Thursday, but tests conducted later Wednesday found "a small fracture" that will take five to six weeks to heal, the coach said.
Tate wore a cast Thursday and says the injury occurred in the third quarter when he was tackled by Saskatchewan's Tyron Brackenridge.
"Brackenridge shoelace tackled me kind of rolling to our sideline and I just went down on it," Tate explained. "It didn't really bother me until before the last drive of the game."
Hufnagel had signed Tate to a three-year contract extension and jettisoned Henry Burris to the Hamilton Tiger-Cats in the off-season.
Tate was going to get his first shot as a starting quarterback in the CFL, but Hufnagel smartly acquired a seasoned backup in Glenn in the Hamilton trade.
Glenn may not be as nimble on his feet as Tate, but the 33-year-old was a solid 4,220 yards in passing for 25 touchdowns and a completion rate of 66.7 per cent.
"We've been in this situation before and we've overcame it, so we'll do the same thing this time," Glenn said.
Glenn led the Winnipeg Blue Bombers to a 10-7 record and wins in both the East semifinal and final in 2007.
Glenn couldn't play in the Grey Cup game, however, because of a broken arm he suffered in the fourth quarter of the East final. The Bombers lost to the Saskatchewan Roughriders.
"Shoot, I've been in that same situation where I was that guy, so I understand exactly what (Tate) is going through," Glenn said.
"At the same time I've got to focus on the task at hand and that's winning the game."
Glenn and Tate split duties in the final two games of the regular season, so the quarterback hasn't had time to collect rust.
"I didn't relax and I've been through this before because I know the significance of being that backup, that No. 2 guy," Glenn said.
"I was always ready and the only difference is I'm taking No. 1 reps this week."
Meanwhile, the Stampeders must prepare for a game they need to win if they are going to play in the Grey Cup on Nov. 25.
Calgary defensive back Keon Raymond says the team hasn't lost sight of that amid the upheaval.
"We come to play football," Raymond declared. "Besides all the other things that's going on outside of football, we still have to line up.
"I don't think it's taking anything away from guys' focus."