It will be the 76-year-old Clark's first TV appearance since his stroke, which forced him to bow out of last year's show.
"I'm not a doctor and I'm not his wife so I don't see him on a daily basis, but he will not be in a wheelchair on the telecast," Seacrest told AP Radio in a recent interview.
Seacrest, who will make his debut as co-host of the New Year's Eve special, said Clark "has gotten better and better each day. I don't think he is a hundred percent but I think he's better than he was last week and better than he was six months ago."
As for Clark's voice, Seacrest said: "It's not exactly as it probably sounded when he was his healthiest and before the stroke, but it definitely sounds like Dick and I think that he's been working on his speech and making sure that it's as good as it can be on the night."
"I know that he is one of the most driven and focused individuals on the planet," the 31-year-old Seacrest said of Clark. "And so when he puts his mind to something and when he wants to do something like this television show and be there for everybody to see him, he'll do it."
Seacrest and Clark will appear from New York, where the ball will drop in Times Square in the traditional countdown to midnight. Co-host Hilary Duff will anchor and perform at the Hollywood segment of the show.
The 34th annual "New Year's Rockin' Eve" will air Saturday starting at 10 p.m. (EST).