ITV's main daytime presenters will all return to the airwaves after their summer breaks on Tuesday, September 1.
The newspaper says that Willoughby has cut short her family holiday in the Algarve in order to complete a mandatory two-week quarantine before she returns to the airwaves.
"Holly accepts that she has to go into quarantine and will follow the rules," said a source.
"Instead of seven weeks away she has had to make it five – but it's what she's had to do to keep the This Morning team safe and to ensure she returns to the show on time."
Morgan, meanwhile, rushed back from his holiday in France last week after the government announced a change to quarantine rules and is due to film two new episodes of Piers Morgan's Life Stories before his GMB return.