The TV presenter - who was forced to pull out of hosting the ITV breakfast show the morning after the National Television Awards because she had lost her voice - reassured viewers she did not have COVID as she apologised for not being back on screen.
Reid explained in a video on her Instagram stories: "Sorry I won't be with you in them morning. Vocal cords affected by mild infection (not C), which I didn't even realise I had! Need to rest them a little longer. See you v soon!
"A quick update on my voice which you can hear is not 100 percent, I feel absolutely fine but the specialist I saw on Friday said not to risk it until it is better. Thank you to everyone at GMB for stepping in and to all of you for your brilliant tips."
She added: "So sorry not to see you tomorrow @gmb. Back in full voice v soon I hope, thanks to specialist treatment and your brilliant tips."
Reid travelled in to the studio the morning after attending the NTA awards, but was replaced by Charlotte Hawkins as co-anchor of GMB when it emerged her voice was not in a fit state to present the show.
Reid appeared via video link-up from her dressing room and croaked: "I'm fine I just can't speak!
"I don't know [what's wrong]. I don't know whether it was the heat inflaming my vocal chords. It's funny because of course it was the NTAs last night and when I got into my cab to leave the driver said, 'You're the very first person to leave. You're obviously not partying.'
"And of course I don't drink, I don't smoke, so there's absolutely no reason I can understand but I've completely lost my voice."
She added: "I'm really sorry. I can only apologise. But thank you Charlotte for stepping in. I didn't want to inflict this on our viewers for a whole three hours."
Hawkins revealed: "The irony of it - we were all there together last night, you left first, you hadn't been drinking anything. I didn't leave as early as I should have done."
And Balls added: "I left with Susanna at nine o'clock. We got in the same lift, we parted at the transport desk. I've got to say your voice sounded fine then, but it's obviously deteriorated over night."
Reid shared pictures of herself at the awards event on her Instagram stories enjoying the evening with various celebrities including her former GMB co-anchor Piers Morgan.
Reid gave up drinking in 2018 after a doctor warned her about weight gain.
Speaking about her sobriety in 2019 she told The Sunday Times magazine: "Seven months on my skin isn't perfect but it's clearer. And so is my head. I am sleeping better."
"I don’t have hangxiety. I don't miss for a minute that feeling of fizzing in your body in the morning, which meant I couldn't quiet relax the day after a big night."
She did admit: "I haven't been entirely dry…there are times you fall back into it."
Watch: Susanna Reid celebrates 20 years working on breakfast television