From The Guardian:
Extra security was mounted and fans were told not to bring bags when United played Charlton. Similar arrangements were expected on Saturday when the club hosts rivals Liverpool, although authorities played down reports that the match might be a target for extremists.
The added police presence followed the arrests and continued questioning of nine men and a woman who were arrested on Monday over an alleged terrorist plot to bomb Manchester.
The Manchester Evening News said tickets for the Liverpool match were "understood to have been recovered" during a series of anti-terror raids on Monday. The claim was strenuously denied by the football club. Police also sought to reassure spectators, saying there was no reason for the games not to go ahead.
A Manchester United spokeswoman said police had not told the club it was a target. "Security is always tight on match days and the safety of spectators is always paramount," she said.