The Red Devils are now facing a second successive Premier League postponement due to the death of Queen Elizabeth II.
Some Premier League games are taking place this coming weekend, after the entire round of matches was cancelled last time around.
The statement read: "Following extensive conversations with the Premier League, Greater Manchester Police and Trafford Council, the decision has been made to postpone Manchester United's Premier League fixture against Leeds United, scheduled to take place at Old Trafford at 14:00 BST on Sunday 18 September. This is due to Greater Manchester Police supporting forces across the United Kingdom at locations and events of high significance following the passing of Her Majesty Queen Elizabeth II.
"The club reiterates that the safety and security of our fans is paramount and, after considering all available options, we are supportive of the decision that was made in conjunction with the relevant authorities. Please note, tickets already purchased for the game will remain valid for the new match date and we will contact ticket holders directly with further information when it is available.
"We appreciate the disappointment and inconvenience this may cause and thank you for your understanding and continued support. The fixture will now be rescheduled and updated details will follow in due course."