The presenters were due to host Sunday night’s show together as usual, but just a few hours before it aired it was announced that Willoughby had the coronavirus.
As the programme opened, Schofield pretended to be startled as he looked at the empty space beside him.
"As you can see Holly isn’t here tonight," he said. "We found out just a few hours ago that she’s tested positive for COVID."
Schofield – who had to miss Dancing On Ice and This Morning after testing positive himself last month - went on: “I know what it’s like to watch this show from home, it is really weird. Holly, get well soon, lots of love.”
The star also posted a message on Instagram saying he was "gutted" to be presenting the semi-final without his co-host.
Unfortunately, Holly Willoughby is unable to host tonight's show after testing positive for Covid-19. Tonight's #DancingOnIce Semi-Final will be hosted by Phillip Schofield and we look forward to Holly returning for our Live Final ❤️ @hollywills @Schofe pic.twitter.com/8a9HPPJtbv
— Dancing on Ice (@dancingonice) March 13, 2022
Earlier, a spokesperson for the ITV show said: "Unfortunately, Holly Willoughby is unable to host tonight's show after testing positive for COVID-19.
"We look forward to Holly returning for the Dancing On Ice live final."
Fans tuning in for the semi-final also said they were missing Willoughby.
"Sad to hear @hollywills tested positive, the show isn't the same without her. Get well soon Holly!" one tweeted.
"It just isn’t the same without Holly!" said another.
One posted: "Phil without Holly is like Ant without Dec… doesn’t feel right."
The semi-final will see BMX racer Kye Whyte, Pussycat Doll Kimberly Wyatt, former Strictly pro Brendan Cole, The Vamps’ Connor Ball and dancer Regan Gascoigne battling to survive a double elimination.
The final of the ice-skating competition was expected to be on 20 March but it has been delayed by a week as ITV has bought the rights to a double-bill of football matches that will air at the same time as the original date.
It will now take place on Sunday, 27 March.
Watch: Connor Ball falls and cuts leg on Dancing On Ice