Brown, 29, was signed from Sheffield in the close season, but suffered a broken thumb in last Sunday’s win over Rochdale – his third major injury of 2009.
He is expected to be out for six or seven weeks, and has already missed long periods with a broken hand and foot injury.
Brown went straight to hospital following Sunday’s game and had an operation on Monday.
He said: “When they X-rayed the injury they found that my thumb bone had gone out of alignment and I had to have an operation to put it back in place.
“They’ve wired the bone in position. I’ve got to go back in two weeks for a check up and then return two weeks after that to check how it’s healed.
“I’m just hoping and praying that I can get back before the end of the season to show what I can do.
“Barry must be wondering what he’s signed because this has been a nightmare season for me. First it was broken hand and then a foot injury. Now it’s my thumb, it’s really frustrating for me.
“The worst thing is that I’ve never had anything like this happen to me in my career before.
“In four years at Sheffield all I suffered was a minor hamstring tweak and I can’t believe what’s happened to me since I signed the Cougars”.
And as a double blow for Craig he’s not able to work because he’s a self-employed carpet fitter.
“It’s not much good for business, that’s for sure,” he mused.
Promotion-chasing Keighley could also be without winger Gavin Duffy for a month, after he pulled out of the Rochdale game with an ankle injury he suffered at work.
Head Coach Barry Eaton said: “It’s not quite as bad an injury as it first appeared. At first we thought that he had broken his ankle.
“But now it looks as though its badly sprained and he could be out for up to a month”.
Eaton was reflecting on what has been an injury hit season for Keighley. He said: “Just when it looked as though we had come through the worst of the situation we pick up two more long term injuries.
“It’s not been the easiest of seasons for us with key players out for long spells with injuries but we’ll keep battling on.”
Eaton will be running a check on winger Lee Mapals, who suffered a bang on his knee during the game against Rochdale.