Friends of the actor, who has been holed up in Byron Bay since the split, revealed he can't face heading back to his Los Angeles home with Cyrus, who was spotted with Brody Jenner's ex Kaitlynn Carter in LA, days after the two were photographed kissing in Lake Como, Italy.
Meanwhile, Jenner came out in defence of Carter on Instagram, saying the pair continued to be "best friends" and that there was "too much negativity" being directed at her.
"I respect Kaitlynn and care deeply about her," Jenner said.
A business associate told The Mail Liam has been "so rocked" by the split that he cannot get his head around focusing on work.
"He is not coming to LA for Killerman anymore even though he had told the film executives that he loved the movie and wanted to go full force into promoting it," the insider said.
"There was a feeling that the premiere was going to be a major summer event with Miley joining her husband. All the signs and talk from his team was that Miley and he wanted to put on a public show of support.
"There was even a plan for Liam to appear on the late night talk shows to promote the film.
"He is deeply upset that things did not work out and stunned at seeing how quickly Miley appears to moved on.
"He is now not in the right head space to step back into the limelight to do any promotion as he knows Miley's name will come up.
"Liam is just surrounding himself with close family to try and heal and see what Miley does next. They want him to stay at home and heal.
"Even the thought of jetting back to LA is painful for him."
The couple have a Malibu home, to which Cyrus has returned with Kaitlynn Carter.
