Paul Nicholls reported Kauto Star to take a "big step forward" on Saturday morning.
The remarkable 12-year-old is rated only 50-50 to make the Betfred Cheltenham Gold Cup on Friday week after a schooling fall.
However the champion trainer, writing in his exclusive column at www.betfair.com/paulnicholls, reported on Saturday morning: "I tweeted that today's Kauto Star's work this morning was, in Clifford's words, a "big step forward" for the horse.
"Kauto had his physio this morning and had an hour on the walker, and you could just tell that he had more of a buzz and a spring in his step, and that a bit of the old swagger had returned.
"So we decided to send him out second lot and he did a strong canter over ten furlongs with What A Friend, and delighted us. And when Clifford pulled up and said "big step forward", he didn't need to add anything. I could simply tell by the smile on his face.
"I cannot tell you how massively relieved I am to see Kauto progressing and going forward. Don't get me wrong, or carried away, because he is not there yet.
"Not at all, and things can change daily. But this was a step in the right direction and I'm much happier, I can tell you. We were going to give him Sunday off but I have decided to keep the momentum going and he will have another canter."
Earlier, Nicholls admitted he faced "the biggest decision I've ever had to make" regarding whether Kauto Star would be allowed to line up in the blue riband in less than a fortnight's time.
No final decision will be made on his Prestbury Park participation until next weekend.
"It's getting better and better every day," Nicholls told Channel 4 Racing's The Morning Line.
"He's never taken a lame step, he's never been off his grub, he looks great and he's cantered every day since it happened.
"He can't talk to you and tell you exactly where it (pain) is, it's impossible to tell. Clifford can just tell by riding him.
"Every day he comes back from work, he always has a roll. He hadn't done that until yesterday morning, so that's a good sign. We're moving forward.
"The idea is to work him hard as normal next week and next Saturday he is due to do a strong piece of work, his last serious gallop, with Big Buck's.
"There are no fitness issues here, we haven't missed any work and he was fit and well.
"Next Saturday will tell us, then I'll have a discussion with Clive (Smith, owner) and Clifford. We'll all have a little input and see if we can come up with the right decision.
"It's a difficult decision, probably the biggest decision I've ever had to make. We've got it right so far this season, we want to try and get it right again."
Sunday Indo Living