At the start of the ITV morning show Schofield, 59, said: "Holly and I were starting to think after doing the show through everything that we may be immune. But it got me and now it's got her.
"It's the weirdest thing watching the show at home. Get well soon, we miss you."
Gibson added: "Yeah, get well son Holls."
Gibson, 37, will join Schofield on the This Morning sofa this week, while mother-of-three Willoughby isolates at home.
As of 24 February people in England are no longer legally required to self-isolate if they test positive for COVID-19, but government advice states they should stay at home and avoid contact with other people, of they can.
Schofield hosted Dancing On Ice alone on Sunday night due to Willoughby's absence.
He told viewers of the celebrity skating show on Sunday night: "As you can see Holly isn’t here tonight. We found out just a few hours ago that she’s tested positive for COVID.
“I know what it’s like to watch this show from home, it is really weird. Holly, get well soon, lots of love.”
He himself had to missed the skating show after he contracted COVID-19 last month.
But Schofield was replaced by Willougby's old children’s television sidekick Stephen Mulhern who joined her to co-host Dancing On Ice.
Gibson, who is a single mum to three-year-old son Reggie-James, performed live on stage with country band The Shires at London's O2 arena, as part of the Country To Country Festival 2022 on Sunday 13 March.
The TV presenter and former Big Brother winner has previously stepped in for Willoughby at the last minute, back in November last year, when Willoughby came down with a stomach bug.
Schofield said to Gibson as they opened the show: "'This is a bit of a first! About an hour ago you were on your way to do our live competitions in Surrey.
"Holly is not here today because she's got a tummy bug. Nothing more than that, she's probably back tomorrow. But you were parachuted in."
Gibson confessed: "I couldn't believe it... I thought they had the wrong number, Phil. I said, 'You've phoned Josie.'"
She added: "How surreal. I've grown up watching the show and now I'm sat alongside you.
"'I've been thrown in the deep end, but I've got the best armbands on the planet. That's what I say.
"I just cannot believe I'm sat here, it is so surreal," she added. "I've grown up watching you, it's just crazy. What an honour."
The Bristol-born TV presenter who regularly appears on the ITV show presenting competition segments, has since co-hosted the show several times.
Watch: Holly Willoughby cries on 'This Morning' for plight of Ukraine