Aston Merrygold was left "mortified" after dropping Janette Manrara head-first during "Strictly Come Dancing" rehearsals.
The former JLS singer "couldn't stop apologising" after one particularly ambitious part of their training session for this weekend's salsa dance went "horribly wrong" and the professional dancer ended up on the floor.
A source said: "It was really nasty. Aston was lifting Janette but it went horribly wrong.
"It left her shaken and she had to be checked over by the team. Fortunately, it looks like she's fine, which is a big relief.
"But it's a confidence knock for them. Aston was mortified. He couldn't stop apologising."
Despite the slight mishap, Janette is confident Aston will get it right on Saturday night (30.09.17) when they perform the salsa to the tune of Luis Fonsi's hit song of the summer "Despacito".
The source said: "Janette was very gracious and doesn't want it to impact him.
"She still trusts him to get the lift right when it really counts on Saturday night.
"Janette has told Aston she believes he can do it but it comes with a significant risk.
"He could very easily kick her in the head in another move they're planning.
"But they are determined to finish top again."
Aston is the current bookmakers" favourite to win this year's "Strictly Come Dancing" and some believe the pair feel "under pressure" to wow the judges with a complex routine.
The source added to The Sun newspaper: "They obviously feel under pressure to live up to their early success and that has led to them coming up with an incredibly ambitious routine.
"But it is dangerous and a lot can go wrong."
After performing with Janette on TV for the first time last week, Aston paid tribute to her on his Instagram account, and admitted he had "so much fun".
He wrote: "Thanks so much for all the support and messages!! Last was amazing but the last couple weeks this lady has busted her arse to make me look comfortable doing ballroom! Thanks to my homie, teacher and dance partner for giving #teamMNM an amazing start to @bbcstrictly "17!!!! Honestly had so much fun and can't wait for this coming week and next sat! (sic)"