Red Devils supporters were already furious with FA’s decision to move the match to a Friday night.
The fourth-round tie will be played under the lights tonight, kicking off at 7:55pm after the game was selected for TV coverage.
It meant supporters travelling from Manchester and the north were forced to plan extra travel arrangements accordingly.
The majority of away supporters are likely to be making the trip using Virgin Trains who run a service from Manchester Piccadilly.
But fans were hit with another obstacle this afternoon when a trespasser on the lines caused Virgin to suspend their services.
They tweeted at 1:28pm on Friday afternoon: “#VTNEW Due to trespassers on the railway at Rugby all lines are blocked. Updates to follow.
This was followed up with: #VTUPDATE Departures are suspended from both Euston and Manchester until further notice. We would advise checking for live updates.”
Some fans then begun to lose their cool in fear they would not make the match or be running behind.
One tweeted: “Unblock it then, what’s on there exactly? Got an FA Cup tie to get to.”
The delayed service that was halted by trespassers then continued on its way, but would no be going all the way to Euston.
Passengers were made aware that they had to terminate at Milton Keynes, causing more complications.
Virgin later confirmed at 2:03pm that lines had reopened.
“#VTUPDATE Lines have now reopened but there may be some residual delays, please check your journey before travelling,” they tweeted.
Some rival supporters mocked the news that services were delayed for Man United supporters.
One tweeted: “Man United fans live down south so they won’t need a train from Manchester to London.”
Another added: “They are all from London anyway so it’s not really an issue.”
A third continued the joke: “Don’t they all live around the M25 anyway?”