British media reported that the Premier League club had hired a former inspector from Greater Manchester Police's specialist search unit.
The Manchester Evening News said the new chief had started work "alongside the club's current senior security team, with an emphasis on counter-terrorism and general security improvements".
The appointment of the unnamed officer at one of the world's biggest and best-supported clubs comes amid heightened global concern after recent attacks in Europe and security breaches at United.
Two stands at the 75,000-seater Old Trafford ground were evacuated just before the start of a league game against Bournemouth in May when a suspicious package was found in the toilets.
The game was called off soon afterwards and the stadium cleared. The package was later revealed to be a fake device accidentally left behind after a training exercise.
Two fans on an official tour of the ground in November managed to hide in a toilet and stay in the stadium overnight in the hope of watching a Premier League game against Arsenal.