The dance duo were in rehearsals for tonight's show (May 7) when Kai Widdrington accidentally kicked his partner Natalia Jeved in the head.
"Natalia has had an ice pack on her head for the last hour and is hoping to be okay for tonight's show," a source told Digital Spy.
The insider added that Widdrington was "mortified" about the accident.
Producers are reportedly concerned that she may have suffered a concussion during the accident.
Kai and Natalia will perform their routine during tonight's second live semi-final alongside the likes of 14-year-old singer Paige Turley and street dancers Karizma Krew.
Ashleigh & Pudsey and Only Boys Aloud were the first acts to make it through to the final last night.
The Britain's Got Talent semi-finals continue tonight at 7.30pm on ITV1.