Kirsty Hair, 20, was with her daughter Kayla McGhee, 2, at Brodie Park in Paisley at around 6pm on Saturday when a pitbull ran up from behind and grabbed the tot by the ankle.
Full-time mum Kirsty said: "I was in the park with Kayla trying to tire her out so she would get a good sleep when she went to bed.
"Then it just all happened so fast. The dog just ran up, grabbed her by her foot and swept her off her feet.
"Then it just started shaking its head, like that way a dog does when it's mauling something.
"It wasn't on a lead and the owner wasn't really to be seen and after it happened, he ran up, put the dog on the lead and ran away.
"I got bitten on the hand but that was more from me trying to pull the dog away."
Kayla was taken to Royal Alexandra Hospital after the attack, and was later transferred to Yorkhill Hospital where she spent two hours in theatre for the wounds to her ankle and foot to be cleaned and treated.
Now recovering at home, the toddler has to wait and see if more medical attention is needed, as the wound needs to be left open in case of infection from the dog's saliva.
Mum Kirsty said: "Her ankle was just shredded and she has puncture wounds as well. She's on painkillers and she's got antibiotics. She's going back to hospital tomorrow.
"I honestly don't know what will be next because we need to wait and see. If it did get infected she would have to go back into theatre."
Police have launched an inquiry to trace the dog and owner.
The dog is said to be a pitbull type and its owner is described as white, in his 30s, around 6ft and slim with short, dark, curly hair.
Officer have been carrying out door-to-door inquiries and are checking CCTV images in a bid to track him.
Kirsty added: "I'm at that park every day, and I've never ever seen him before. It was horrible that it still did happen, but Kayla was lucky because it was just her foot. This dog is still out there and the next time it could kill a baby.
"And usually these dogs go for the head or the face, so she was very lucky."
Anyone with any information is asked to contact officers on 0141 532 5900.