Lindsay, who is partnered with singer and actor Jordan Fisher this season, has suffered a painful injury that could prevent her from dancing on Monday night's show, People reported.
"Lindsay injured her knee during camera blocking rehearsal Sunday morning while working on a number with the Troupe," a Dancing with the Stars source told the magazine.
In case Lindsay can't perform in the next show on November 13, previously-eliminated professional dancer Sharna Burgess will fill in for her.
Sharna -- who was paired with retired NBA star Derek Fisher for Season 25 -- would therefore dance two full routines with Jordan, who has been a frontrunner in the Season 25 competition this fall.
"Lindsay is hopeful she'll be cleared to dance tomorrow but it will likely be touch and go until showtime Monday," the DWTS source continued.
In a video obtained by People, Lindsay explained how her injury occurred.
"I was practicing the pro number and I literally just stepped up onto a stair and it felt like my whole leg gave out and stopped working and I thought it was just a one-time thing and then it happened a couple more times, just doing simple things," Lindsay said in tears during a physical therapy treatment.
"It's frustrating," she added, "because it's the semifinals and I want to dance it with Jordan, and I just hope this doesn't stop me from doing that."
The bubbly blonde is the only professional partner left in the competition this season who has yet to win a mirrorball trophy. Fans have speculated her chance of claiming victory this season with Jordan is great, so her injury is pretty devastating.
According to Dancing with the Stars spoilers, Lindsay and Jordan were preparing to dance an Argentine tango together to "Brother" by NeedtoBreathe featuring Gavin DeGraw, followed by the reprisal of a memorable dance from the show's history.