The actress portrayed a paramedic Emergency Medical Services captain, opposite Rob Lowe, on the TV series, which debuted earlier this year and she was planning to reprise the character for a second season.
But she has opted not to risk her health and travel from London, where she lives with her family, to Los Angeles and back to film the show.
TV bosses tell Deadline her role will not be recast in the hope that Liv's character will return in the future.
"What a thrill it was having a movie star of Liv Tyler's stature to help us launch the first season of '911: Lone Star'," series co-creator and executive producer Tim Minear tells the outlet. "We loved working with Liv and will be forever indebted to her for her haunting, powerful portrayal of Michelle Blake. While we were able to tell a complete chapter in Michelle's story... there are more stories to be told. The door here will always be open for a return."
The news comes days after it was announced Gina Torres is joining the show as a Paramedic Captain.
The uncertainty surrounding travel amid the ongoing coronavirus pandemic has reportedly made it difficult for Tyler to continue working on the "9-1-1" spin-off. She lives in London with her partner and children, including a 5-year-old and a 4-year-old. In the last season, her kids joined her in L.A. during vacations and she went back and forth at the other time so that she wasn't being away from her children for long.