The actress appeared on the show on Monday via video link and was telling Alex and stand-in co-host Gethin Jones about her lockdown experience.
Michelle said she has been filling her time in lockdown by gardening when she accidentally made the cheeky innuendo.
The quip left both Alex and Gethin with the giggles while Michelle carried on talking blissfully unaware.
It all started when Gethin asked Michelle, who has been documenting life in lockdown on her Instagram, how her gardening skills were coming along.
What did Michelle say?
"I bought a hedge trimmer from Amazon," she explained.
She added: "Let me tell you now, my garden is completely bald!"
At this point Alex and Gethin burst into laughter while Michelle carried on chatting about her gardening skills without realising what she'd said.
Michelle continued: "I got carried away and now I’m obsessed with it."
She added: "To be fair I didn’t do all the garden, that was an oldish picture," referring to an Instagram post.
Viewers laughed at Michelle's cheeky innuendo on Twitter.
"Michelle Keegan announcing she has a bald garden on The One Show this evening was a real treat," one viewer said.
"Didn’t see that one coming at all."
Another added: "Michelle Keegan is going to regret that statement on The One Show about her garden being completely bald.
"Even Alex Jones is giggling."
"Michelle Keegan on The One Show," a third said. "I have brought a hedge trimmer my garden is now totally bald... Alex Jones lost it."
Meanwhile, Our Girl star Michelle addressed rumours she will replace Holly Willoughby as a team captain on Celebrity Juice.
At the weekend, Holly announced she was quitting the show after 12 years to spend more time with her family.
However, it looks like no official offers have been made to the actress as yet.
Michelle addresses Celebrity Juice rumours
She said on the BBC show: "Celebrity Juice. Well I can officially say that’s not true unfortunately.
"Don’t get me wrong, I love the show, I find it hilarious but no, that’s not true."
Michelle recently quit Our Girl after four years of playing Georgie Lane.
Now the BBC show has finished on air, she confirmed that the door has been left open and fans may see Georgie back in the army one day.
She said: "The door has been left open for Georgie. I absolutely love the show, I’m so proud of it. Hopefully you’ll see Georgie again."
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