The seven-month-old tot was in her mum’s arms as they waited in the fast food chain when the man struck but initially her parents did not notice any visible injuries.
Hours later they noticed a bump on the baby’s head and a scan at an east London hospital showed a small fracture and bleed on the brain.
Police investigating the altercation on June 18 in McDonalds, East Ham, east London, are now trying to establish if the assault was accidental.
They are hunting a wheelchair bound man described as Asian wearing a black jacket and aged between 15 and 25-years-old with a foam cast on his right arm.
Detectives are also trying to trace a black woman, believed to be the man’s carer, who is roughly 40-years-old and was wearing a beige coloured jacket and carrying a brown handbag.
The baby was kept in hospital overnight and has now fully recovered.
A Metropolitan Police spokesperson said: “On Saturday, 18 June, at the McDonalds restaurant in Gallions Reach Shopping Centre, E6 there was an incident involving a baby girl - aged seven months - and a wheelchair user between 2pm and 3pm where the wheelchair user allegedly struck out hitting the baby.
“The baby was being held in her mother’s arms as she stood in a queue in the restaurant.
“At the time, her parents believed there were no visible injuries but later that afternoon, they noticed a bump on the baby’s head.
“They took the child to an east London hospital where a scan showed a small fracture to the skull and a bleed on the brain.
“The baby was kept in hospital overnight but discharged the next day. The baby has now fully recovered.
“Officers were called by the parents when they attended the hospital.
“Detectives are trying to determine whether the alleged actions of the wheelchair user were accidental.
“All lines of enquiry have so far been exhausted with detectives studying CCTV at the restaurant and speaking to various agencies to identify the people involved.
“Detectives are now releasing a CCTV image of a witness they wish to trace - a woman who they believe to be the wheelchair user’s carer.
“She is described as a black woman, aged approximately 40 years old of large build. She was wearing a beige coloured jacket and carrying a brown handbag.
“The man in the wheelchair is described as Asian, aged between 15 and 25 years. His right arm had a foam cast on it. He was wearing a black jacket and was of large build.
“Detectives are also keen to hear from anyone who was in the restaurant at the time of the incident and remembers witnessing it.”