A five-year-old boy will need surgery after being knocked down by an off-road bike while playing football.
The child suffered leg and lip injuries after being hit by the bike on playing fields on Kings Road in Oldham on Thursday evening, police said.
A 17-year-old was arrested and later released under investigation.
Greater Manchester Police said it had stepped up its efforts to stop the use of illegal off-road bikes by drafting in extra resources.
Ch Insp Abigail Cronin said: "We understand the frustration of the local community with this type of anti-social behaviour and we want them to know that we are aware of it and have a plan in place to ensure that it is dealt with appropriately."