Emergency services were called to The John Russell Fox pub in Andover High Street on Saturday night, when a teenager was injured inside the closed building.
Police were concerned for the teenager's mental health after friends had rescued him from the building site after he appeared to have harmed himself.
A spokesperson from Hampshire Police told Andover & Villages, "The initial report was that of an intruder inside the building site at the John Russell pub in the High Street at around 9.30pm on Saturday, 18 November.
"Four youths were found nearby who had rescued a friend who was injured inside the site.
"The 17-year-old has been treated in hospital for his injuries and is making a recovery."