Teigan Campbell from Coventry in the West Midlands received the 'scare of her life' after she discovered that her daughter Poppy was caught in a cord from her cot's mobile.
Poppy, who is nine months old, was left with a visible mark where the cord had cut into her digit - and mother Teigan said she wouldn't have been surprised if she'd lost a finger.
Teigan has now warned other parents against placing toys above their child's cot - no matter how soothing they are for little ones.
In a warning to other mums posted on Facebook, Teigan said: "Last night I had the biggest scare of my life, Poppy usually has her mobile (she's had since a newborn) on to settle her down when she's going down.
"For about half an hour after she went to sleep, I didn't hear a peep out of her until I was in the shower and she started crying randomly, which is really unusual for Poppy to wake in the night now.
"When I went to check, my daughter had the string of the mobile wrapped around her finger, so tight I thought my child was going to lose a finger, that tight in fact I was struggling to remove the string at the start!"
She explained that she was left to console her injured tot and even had to phone the NHS to see what she should do.
She added: "I cried my eyes out and massaged her finger as much as I could to get some circulation back in her finger and rang 111 for further guidance.
"I'm just so lucky and grateful that I ran into her room at the right time and that my daughter still has a thumb left!!
"This is just a reminder and a warning for all mums out there to be extra vigilant when buying cot mobiles for their little ones and go for a thicker string option (also look out for hairs wrapped around fingers and toes!)
"I really did get the shock of my life. Ps the mobile is now in the bin and she won't be allowed it back."
Hairs can also be a danger to tots as they can wrap around fingers, toes, or a baby's genitals, cutting off the blood supply.
Strands of hair are so thin they often go unnoticed, but so-called Hair Tourniquet Syndrome can cause major damage.
The Lullaby Trust, a charity that raises awareness for sudden infant death syndrome (SIDS), said mobiles should always be kept well out of reach of babies.
