Mr MacIntyre, 39, was running in Hampton, south-west London, on Sunday morning with a personal trainer when a man began kicking and punching him, shouting: "You should not have done it!" After a struggle his attacker, who was said to be a white male in his thirties, ran off.
Mr MacIntyre said the incident was "a completely unprovoked attack, which took me by surprise." A police spokesman said: "We are keeping an open mind about the motive."
The reporter infiltrated the notorious Chelsea Headhunters as part of his series MacIntyre Investigates in 1999. As a result, two members of the gang were jailed.
The reporter has received death threats from people aggrieved by his exposes.Reuse content