Chambers has been training with his new team-mates
Castleford say sprinter Dwain Chambers is at least a week away from tasting his first competitive rugby league action after joining the club on trial.
There had been speculation Chambers would be thrown in at the deep end against St Helens on Sunday despite never having played the sport before.
"Dwain's not playing on Sunday. I wouldn't do that to him," said Tigers coach Terry Matterson.
"His safety is important. You can't have someone who is not prepared."
At Monday's news conference to announce Chambers' arrival, Matterson suggested, tongue-in-cheek, that his side's injury problems were such that he might be forced to give the athlete an unexpected debut.
But Matterson now insists Chambers will not even be considered for the reserves, who play a curtain-raiser to the Super League game.
"I think that would be dangerous, to be honest, and I don't think he or the club can afford that," added Matterson.
He doesn't look completely out of place
Cas coach Terry Matterson
Chambers, who completed a two-year drugs ban from athletics in 2005, has spent the last few days training with his new team-mates.
"He's been really good. It's been a breath of fresh air," said Matterson, whose side are bottom of the Super League table with just one win all season.
"We're in a tough place at the moment and he's come along with a smile on his face. He's doing something that's foreign to him and he's enjoying it.
"The reality of it all is that it's going to be a tough ask, there is no doubt about that.
"But he's fast. I don't think I've ever seen anything quite as fast in my life.
"The stamina part is going to be a bit of an issue and it will be interesting to see how he goes in a contact session but we're not ready for that yet.
"That will probably come next week. We've got to make sure we get a gum shield and headgear for him.
"He caught a few bombs (high kicks) on Wednesday and he looked OK. His actual co-ordination is not too bad.
"Catching and passing, that takes time, but he doesn't look completely out of place."
Chambers said the decision to ease him into the sport was the right one.
We'll see what my true colours are when I get out there and play
"I feel more comfortable about playing for the reserves because it takes a bit of the pressure off me," he said.
"It would allow me to get a feel for a game I have never played before. But the training is going well. I think I'm a natural because I have taken to it like a duck to water.
"But we'll see what my true colours are when I get out there and play."
Amateur club Methley Royals, who operate in Yorkshire League Division Four, offered Chambers the chance to get his first taste of the sport.
The Royals asked for permission to use Chambers in their next match against Burley Lions, provided he paid his £3 subs, but Castleford declined the invitation.
Methley vice-chairman Phil Hodgson said: "Our offer remains open.
"The more you think about it, the more it makes sense. Dwain Chambers would gain an insight into rugby league which would, without doubt, stand him in good stead for the challenges ahead."