Officers were called to the westbound carriageway, between junctions 7 and 5, shortly after midnight in the early hours of this morning (Sunday 18 April).
Enquiries remain ongoing to establish exactly how the 17-year-old boy came to be on the motorway and how he became injured.
Police are appealing for anyone who saw any pedestrians in this area of the motorway around this time, or perhaps saw anyone on the Botley Road bridge which runs overhead.
In addition, we would like to appeal to anyone who may have been a pedestrian on the motorway at this time and has any information.
Were you walking along the motorway at this time? Were you with this person or did you see them? Please be reassured that you are not in any trouble, we are seeking any witnesses who can help us establish what happened.
As a result of this incident, the westbound carriageway between junctions 7 and 5 is closed, and a closure is in place on the overhead Botley Road bridge. These closures are likely to remain in place for a few hours.
Anyone with information about this incident is asked to contact police on 101, quoting incident 24 of today’s date.
Alternatively, you can contact the independent charity Crimestoppers 100% anonymously on 0800 555 111, or via their anonymous online form at crimestoppers-uk.org