The "Cry Pretty" singer detailed the incident to Bobby Bones, telling the radio personality that the "didn't know how things were going to end up."
"I was taking the dogs out...and I just tripped," the 35-year-old said on Bones' radio show on Thursday. "I went to catch myself and I just missed a step."
Underwood said if it weren't for that "one step" she would have been "perfectly fine."
"It was one step that messed everything up," she explained.
Bones asked Underwood where she had her stitches and she said "around my mouth."
At first, the country crooner didn't think there was much damage.
"I thought I just busted my lip. Then I walked inside and took the dog leashes off and took my coat off and went to go survey the damage and was like, 'Oh, no!' It wasn't pretty," she said on Sirius XM The Highway's Storme Warren Show.
The scar, which fans couldn't make out during Underwood's performance at Sunday night's ACM Awards, was noticeable during her interview with Bones.
Because Underwood wasn't sure what the damage would ultimately look like, she warned fans after the incident that she might not look the same, although she explained Thursday that she's been "very fortunate in the healing process" after Bones pointed out she looks pretty much looks the same.
"I was at a point where I didn't know how things were going to end up. I didn't know what was going to go on. I didn't know what it was going to heal like," she told Bones.
She said she feared bumping into fans in public and that they would post a photo of her on social media, causing people to wonder "what happened" to her face.
"It was important to me as I started resuming my life again, and going to the grocery store, and taking my kid to school, and stuff like that. I was like, 'OK, somebody's going to creep on me at the grocery store.' And you know people are going to be like, 'What happened?' when they post it on Instagram."
But her fans weren't the only ones she was afraid of alarming; she even went on to reveal that she was afraid of scaring her and NHL husband Mike Fisher's 3-year-old son, Isaiah.
"I was worried he would be scared of me," she recalled. "But now if I put makeup on, he's like, 'Mommy, your boo-boo's all gone.'"
Underwood said while Fisher was ready to put on his nurse's hat to help her recover, she was reluctant to let him help too much.
"He's all right [as a nurse]. I mean, I'm really terrible at letting anybody help me with anything, to be honest," she admitted. "I'm probably not a very good patient because I'm like, 'I can do it. I'm not completely broken. I can do this.' I'd say the hardest part was my wrist. Like, I can't use my appendage, and I'm trying to pick my kid up and make food and do mom stuff."
Underwood will next perform at the CMA Fest in Nashville on June 8.2comments
"Cry Pretty" will be included on her upcoming album of the same name, which hits stores on Sept. 14. It will be Underwood's first record on Capitol Records Nashville.
Photo credit: Jason Kempin / SiriusXM