The in-form forward had hoped to watch his old team but a prior commitment means he will not be at Cougar Park to support his fellow Cumbrians.
Donaldson revealed: “It’s Brett Kearney’s little girl’s birthday party on Saturday, so I’ve been invited to that.
“I’m disappointed not to be able to go to Keighley because all my friends still play for Wath Brow and whenever I’m back home I’m back in that environment all the time.
“I think they have a chance of beating Keighley.
“Over the years they have beaten Whitehaven, who were in the Championship at the time, and they have played some big clubs such as Featherstone.
“Hopefully they can cause an upset this weekend and I'll certainly be keeping my fingers crossed for them.”