The Channel 5 news anchor compared it to leaving football great Lionel Messi on the bench for a World Cup final.
He was paired with the Ukrainian, 34, in 2021 and formed one of the show’s most sensational duos.
The decision to shut her out of this year’s contest, which starts on Saturday, has been met with a chorus of disapproval on social media.
And Dan, 46, wrote on X, formerly Twitter: “Strictly is such an amazing show and it’s almost time for the new series, what a great line-up this year.
“All the pros are great but gutted to hear that @nadiyabychkova hasn’t got a partner.
“I’m sure she’s still looking forward to being part of the biggest show on TV.
“But it feels like putting Messi on the bench for the World Cup final!”
Nadiya was thought to be a shoo-in to be paired with a celeb, as she has since she joined six years ago.
It was a particular surprise given the BBC used her so predominantly in the publicity to drum up interest ahead of the start of the 21st series.
She will still take part in group dances but fans are bewildered by her being denied a starring role with a partner — a sentiment said to be shared by Nadiya.
An insider said: “She’s terribly upset and so confused as her star wasn’t just rising, it was soaring.
“If she has done anything wrong, she has no idea what it is as she’s always dedicated herself to Strictly.
“Of course, she understands that among the dance troupe there are always more dancers than there are pairings.
“So it’s a little bit like rotating players in a football team.
“But many viewers will be wondering why someone who’s widely regarded as a striker ends up sitting on the subs’ bench when they have so much to offer the squad.”
Nadiya, who started dating fellow pro Kai Widdrington, 28, after they met on Strictly two years ago, has built up a strong following since she first appeared in 2017.
Fans took to X to express their disbelief that Nadiya, a ballroom and Latin world champion, would be taking a backseat, with some suggesting they will stage a boycott.
One said: “Not giving Nadiya a partner? Strictly, you’re dead to me this year.”
Another said: “Shocking! She is immensely talented not to mention breathtaking.”
Nadiya has enjoyed mixed success on the show but was a particular hit after being paired with Dan.
She managed to transform the newsman from a clumsy try-hard into a competent mover.
They won over viewers — if not always the judges — and finished in fifth place.
This year, she was widely expected to be paired up with EastEnders star Bobby Brazier, 20, who, at 6ft 2ins, required a tall pro like Nadiya.
So there was shock when the pairings were leaked by someone who saw a pre-recording of the launch show.
Nadiya reveals in the new Radio Times how hard she’s worked on Strictly, including sacrificing crucial moments with her daughter, Mila, six.
Nadiya told the magazine: “I couldn’t be there for my daughter’s first day of school because of Strictly. They are crazy hours.”
Nadiya’s upset may be brought into sharper focus if Kai is placed with a celeb when the pairings are officially revealed on Saturday.
He sounded pleased after recording the “pairing up” launch show.
Also speaking to Radio Times, Kai said: “In true Strictly fashion, it’s a big, spectacular opening dance.
“We do an amazing dance with lots of glitter and confetti.
“Welcome to Strictly 2023 — in a nutshell.”
A spokeswoman for the BBC declined to comment.
