A man accused in the assault of a five-month-old baby may have left Ontario, Toronto police said on Thursday after arresting a man they suspect helped him evade capture.

Officers arrested a man they suspect helped Ronnie Munoz-Hernandez leave the province after he dropped his girlfriend's infant off at hospital with life-threatening injuries.

Police say Juan Neira-Penaloza, 30, helped Munoz-Hernandez leave the province.

Munoz-Hernandez disappeared more than a week ago after he and his girlfriend dropped off her son at Toronto's Hospital for Sick Children with serious injuries.

The 21-year-old man had recently moved into the family's west-end apartment. He was home alone with the boy two weekends ago when the injuries allegedly occurred.

It wasn't until the next day that the child's mother found the boy unresponsive and took him to hospital.

After the boy was taken in by emergency doctors, Munoz-Hernandez quietly walked out of the hospital.

The boy is still in critical condition and remains on life support. The child's aunt said the infant had to undergo three hours of brain surgery.

Police are seeking Munoz-Hernandez on a charge of aggravated assault.

Neira-Penaloza faces the charge of accessory to aggravated assault. He was scheduled to appear in court Thursday.