The device discovered which caused Manchester United's Premier League match with AFC Bournemouth to be postponed was a dummy left by a training company, police have confirmed.
Old Trafford was partially evacuated around 20 minutes before the scheduled kick-off and the game was abandoned shortly afterwards as Greater Manchester Police (GMP) sniffer dogs and bomb-disposal teams were drafted in to deal with an "incredibly lifelike explosive device" in the north-west quadrant of the stadium.
A controlled explosion was carried out at approximately 1645 GMT, with GMP confirming that the device - reportedly strapped to a gas pipe - was "not viable".
Players and officials from both clubs were escorted from the stadium, they are scheduled to meet again to fulfil the fixture on Tuesday May 17.
But inquiries are due to be launched as to how a dummy used in an exercise was allowed to be left behind.
GMP's assistant chief constable John O'Hare said: "Following today's controlled explosion, we have since found out that the item was a training device which had accidentally been left by a private company following a training exercise involving explosive searching dogs.
"Whilst this item did not turn out to be a viable explosive, on appearance this device was as real as could be, and the decision to evacuate the stadium was the right thing to do, until we could be sure that people were not at risk.
"I would also like to thank all those involved in the operation today for such a professional response, which includes police officers, stewards, MUFC staff, media representatives and commentators and the Bomb Disposal Team."
United's executive vice chairman Ed Woodward added: "The safety of fans is always our highest priority.
"I'd like to thank the support from the police which was first class and the impeccable response from fans of both teams.
"The club takes security very seriously and staff are regularly trained with the police and emergency services to identify and deal with these incidents.
"We will investigate the incident to inform future actions and decisions."
All other Premier League matches kicked off at 1500 GMT as expected.
Manchester City drew 1-1 with Swansea City to effectively guarantee they will finish above United in fourth, with Louis van Gaal's side requiring a 19-0 victory in the rearranged match with the Cherries to overtake their city rivals and qualify for the Champions League.