Coach Tim Burke said Thursday the doctors decided Pierce was still not fit to return to the field after he received a concussion in a game against the Toronto Argonauts on Sept. 29.
Burke said he has no firm idea when Pierce might get the nod.
"I don't. I'm hoping he will, soon," said the interim head coach, who will go with backup Joey Elliott when the Calgary Stampeders visit Saturday.
The Bombers (4-10) lost 44-3 to the Stampeders (8-6) when they met last month.
But Elliott now has two wins under his belt this season subbing for Pierce , including Monday's 27-22 upset in Montreal. He also posted an earlier victory over the Ticats, when Pierce was out with an injured foot from July to September.
Burke is impressed with the young quarterback's growth and the way he led the offence Monday in Montreal.
"He really did a great job making decisions and I think he's learned to let plays develop and not just chuck the ball down real quick," he said.
"And he was in command of the game. I thought he managed the game really well. That tells you he's not just concentrating on what he has to do, he's concentrating on what the offence has to do."
Burke says another good game this week would be a confidence booster for the team as well as Elliott, but he still wouldn't say another win might earn him a starting spot if Pierce is ruled healthy enough to play.
"Let's just wait till it happens, then I'll give you an answer," he said.
That's a little less definitive than he has been in the past, when he said the team would go with Pierce as soon as he's fit.
The Bombers also included another quarterback in their moves this week to bolster their practice roster.
Quarterback R.J. Archer, 25, was signed by the NFL's Minnesota Vikings in 2010 and spent time on their regular and practice rosters before being released.
More recently the six-foot-two, 220-pound pivot played in the Arena football league and was in camp for the Detroit Lions until he was released in August.
Burke downplayed any significance to the move.
"You're always bringing in guys. We brought in a quarterback, an offensive lineman . . . two defensive backs. What does that tell anybody on the team? It tells them you're always trying to find somebody better."
Archer said he's happy to get the chance and he knows a little about the Canadian game.
"I knew the basic rules and everything, I guess that's more than some people," he said.
"It's still football. There's a bigger field. Obviously I've played some arena football which is a tiny field."
Elliott was gracious in welcoming the new guy. The Bombers currently carry four quarterbacks — Alex Brink and Justin Goltz in addition to Elliott and Pierce.
"He's a nice guy," Elliott said. "Glad to have another guy around. He's going to be learning a lot in the next few weeks."
It's a short practice week, made even shorter by the uncertainty over who the starting quarterback would be.
"All quarterbacks are going to have to bury themselves in the game plan and be ready to go," said Elliott.
As for Pierce's likely return as the starter when he's finally declared fit, he was pragmatic.
"I'm glad to get another opportunity, you never know," he said. "Buck's our franchise guy and whenever he's healthy he'll be ready to go."
On Thursday the Bombers also added man James Carmon, a six-foot-seven, 320-pound offensive lineman, to their practice roster. He was cut by the Buffalo Bills in the pre-season.
Winnipeg will face the Stampeders without receivers Kito Poblah, Cory Watson and defensive linemen Alex Hall and Bryant Turner.