Winnipeg Blue Bombers coach Tim Burke said Thursday the decision was based on "a collaboration of data, it wasn't just one single test," and he didn't know when his starting quarterback would return.
"It's really close but I'm not going to get into the predictions of when he's going to come back, hopefully it will be next week."
That means Joey Elliott will get another start.
"We changed the package a little bit more to suit him as opposed to buck so hopefully he'll have a good game for us," said Burke.
The first-quarter hit by Toronto Argonaut Brandon Isaac that caused the concussion continues to have repercussions inside and outside the Bomber dressing room.
Isaac was fined for the hit but three Bombers were also fined. Offensive linemen Steve Morley and Justin Sorenson were nicked for going after Isaac in retaliation and defensive back Jovon Johnson for what he said later about the hit.
Johnson suggested the Argos were told to go after Pierce.
Morley, a seven-season CFL veteran who has played the last four in Winnipeg, said Thursday that's exactly what the players had been told previously.
"Our coaches told us in the past that this defensive co-ordinator has targeted Buck so we knew going in," said Morley.
"Jovon's just saying what he's already been told."
But Burke says he doesn't believe that to be true and it isn't something he or other coaches would have said.
"Steve should keep his mouth shut because he doesn't know what he's talking about," Burke snapped when asked about Morley's remarks.
"I'm a personal friend of Scott Milanovich and I know he would not ever condone anything like that."
As for the $300 per-player fines assessed the Bombers, Pierce has offered to pick up the tab.
Burke didn't take issue with the player fines assessed the Bombers and, contrary to what Isaac has said on Twitter, insisted his fine was larger.
The players, however, weren't that impressed with the CFL's reaction.
"It's in hockey, you have to have enforcers out there to take care of the top players," said Morley.
"If things aren't going to be done about it you know, you hate to say it, but some of the guys are getting upset with it and have to take matters into their own hands."
Morley said Pierce has told the three he will pay their fines.
Burke also tried to clarify Thursday what he said had been an incorrect interpretation of Pierce's remarks earlier.
Pierce said he returned to Saturday's game for part of the second quarter even though he had a headache, which could be a symptom of a concussion.
Pierce and the team have been criticized for allowing that to happen.
"Buck was quoted as saying he had a headache when he went into the game. He said it to me the way be probably said it to you guys, like it was a headache, but he meant that he had jaw pain and facial pain," said Burke.
"He was cleared to go back in because he did not have any symptoms that affected his brain."