Cougars have seen highly-rated young forward Toby Williams move to LHF Healthplan National League Two rivals York City Knights.
The robust prop/second-row, 20, burst on to the scene at Keighley last season, having made his debut for Peter Roe's men.
Williams' powerful-running style proved a big hit with the Cougars crowd and the Academy product established himself as one of the club's emerging stars.
But he has turned down their offer of a new deal and accepted a two-year contract with York, who are newly relegated from National League One.
Player-coach Barry Eaton said: "It's disappointing. We wanted him to stay but Toby wanted to move on.
"He did really well for us last season and had a massive impact. He's got great power and purpose when carrying he ball.
"Toby needs to improve areas of his game to become a better player but he's definitely got enough in him to play higher than National Two.
"It does need a bit more commitment from himself but I'm sure he's got a big future and we wish him all the best."
Cougars are busy trying to strengthen their own squad ready for 2007.
Eaton has secured the services of forwards Chris Redfearn, Simon Bissel and Greg Nicholson but is continually speaking to more targets.
"They are still in the early stages and nothing's been confirmed yet," he said.
"We've got to make sure they are right for us and they want to come here for the right reasons.
"It's good to know we've already got three new signings on board and I've spoken to another half-back, a three-quarter and others.
"Pre-season training starts on Tuesday and we have got a healthy amount of players already signed.
"We've probably got a squad of about 25 so far and there'll be some more coming down on trial from the amateur game.
"We'll probably be looking at another couple of props, a half-back for some more competition there and a three-quarter but we're not going to rush anything. There's a long way to go yet before the season starts."
Meanwhile, stand-off Adam Mitchell - who missed all of last season with a double leg fracture - is ready to give Cougars a major boost.
Eaton explained: "He's on his rehab programme now, having got the all-clear from the specialist to resume training. We're hopeful he'll be fit for the start of the campaign.
"Adam's got to try and build his strength up in his leg between now and Christmas and, if he can get through this hard work, he will be like a new signing."
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