Heidi Reeve, 24, said her three-year-old daughter, Gracie-May, collapsed to the ground in ‘agony’ after the collision.
The pair were walking along a shared-use path near Landport Adventure Playground when a man hit the youngster and cycled away just after 4.30pm.
Heidi, a stay-at-home mum-of-two, of Grove Road North in Southsea, said: ‘We were just making our way home from Asda.
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‘Gracie was stood right next to me and this man came towards us and hit her. He must’ve drunk so much because he was reeking of alcohol.
‘I tried to get her to stand up so I could check her, but she was crying – then I noticed the shape of her leg. It looked disgusting.’
After ‘wobbling’, the hit-and-run cyclist sped off toward Arundel Street and Heidi called her parents for help.
The family hailed down a passing police car and called an ambulance to Somers Road, where they sat Gracie-May on a wall near Southsea fire station.
She was then taken to Queen Alexandra Hospital, where doctors attempted to manipulate her right ankle into place and applied a cast.
Heidi said: ‘After it happened I was so angry and I was shocked. I thought how could someone do that to a child?
‘It happened so quickly that I don’t know what kind of bike the man was riding or what he looked like.
‘He didn't even say anything afterwards – he just biked off.’
The injury meant Gracie-May’s third birthday party at Canoe Lake on Saturday, August 1 had to be cancelled.
Heidi, speaking after the incident on July 28, added: ‘Now she’s driving herself insane because it’s the summer holidays and all she wants to be doing is playing at the beach with her friends.
‘Thankfully she is alright, but we just can’t do anything.’
A spokesman for South Central Ambulance Service confirmed Gracie-May was given initial treatment in Somers Road, before being taken to hospital.
A Hampshire Constabulary spokeswoman added: ‘We were called by Scas at 4.55pm on Tuesday, 28 July to reports of a collision on Somers Road between a cyclist and a child.
‘The victim… was walking with her mother on Somers Road, Portsmouth, when the cyclist collided with her. The cyclist did not stop at the scene.
‘The girl has a serious injury to her ankle.
‘Anyone with information is asked to phone 101 with the reference 44200282999.’