The Newcastle-born midfielder has trained for the last month with Darlington and told manager Steve Staunton he would return to The Northern Echo Arena.
He left 18 months ago for Rochdale, but was a free agent having been released last month, and Staunton told the media last week the 26-yearold would put pen to paper on a six-month deal.
However, Keltie this week began a trial with Lincoln and has instead agreed to join Chris Sutton’s side who are two are places above Darlington in League Two.
Keltie was due to rejoin Darlington on Monday, but he failed to answer calls from Quakers and it transpires he was in Lincolnshire with the Imps.
A frustrated Staunton explained: “Through his agent Clark agreed to sign last week. He had previously agreed to go to Lincoln for a couple of days trial and he had to honour that.
“I’m disappointed he has gone to Lincoln, especially as we had agreed terms. But there’s not much we can do about it now.”
Staunton will now turn his attentions to other targets, including Irish right-back Simon Madden.
The 21-year-old, a former trainee at Leeds United, will sign today having left Shamrock Rovers where he was a team-mate of fellow new boy Tadhg Purcell.
Staunton hopes Madden will be joined in a new-look defence by Darlington-born Alan White who is surplus to requirements at Luton Town.
“We know about Alan’s situation at Luton and we are actively looking into it,” said Staunton, who was speaking last night during a fans’ forum at The Northern Echo Arena.
“We know Luton are looking to offload three or four players and we are speaking to their manager.
“There’s not much more I can say on that because we are still speaking to the Luton manager. But he is a player we are interested in.”
Having last week recruited Gary Dempsey and Purcell, plus Madden today, Staunton last night admitted he wants to bring in more players ahead of Saturday’s home game with Aldershot Town.
He added: “We’ve got three new faces in so far in January and, hopefully, we’ll have two or three more before the weekend and we won’t be finished there.
“I’m looking to make two signings next week and then we should be done, although we could maybe bring one or two on loan after that if need be.”