Richard Arnold’s position as the Manchester United chief executive is under increasing pressure over his handling of the club’s investigation into Mason Greenwood.

United announced on Monday that Greenwood would be leaving Old Trafford after a six-month investigation into the striker’s conduct. The club faced a fierce public and internal backlash to the prospect of Greenwood being reintegrated into the first-team squad, which Arnold said had been considered, and is now helping the 21‑year-old to find a new employer.

Gary Neville described United’s process as “horrible” and evidence the club lack authoritative leadership. Welfare charities and United fans have called for Arnold to resign, including Rachel Riley, the Countdown co‑presenter, who received severe online abuse after saying she would stop supporting United if Greenwood was allowed to return. Riley has accused United and Greenwood of gaslighting people with their statements confirming the forward’s departure.

In an open letter to supporters Arnold said: “While we were unable to access certain evidence for reasons we respect, the evidence we did collate led us to conclude that Mason did not commit the acts he was charged with.”

Greenwood said he was cleared of charges of attempted rape, controlling and coercive behaviour and assault. The charges were dropped by the Crown Prosecution Service in February after key witnesses withdrew their cooperation from the investigation.

Riley told the News Agents podcast: “The statement that was put out proclaimed someone innocent from a position that they didn’t have any authority to do. That was way beyond the remit of Manchester United to even look into the criminal guilt or innocence, never mind the civil level of guilt or innocence.

“I think it’s gaslighting for people to have two statements saying, Mason Greenwood himself saying he’s been cleared of all charges, which is not the case, the claims were dropped because the key witness dropped out, and they [United] claim new evidence. It puts wind in the sails of people who think they can get away with abuse everywhere. And I think for victims, it’s a slap in the face. It says you’re better to keep quiet.

“I’ve never been more ashamed of the club. I think it’s just a disgrace. And they had another opportunity to make it right, make a good statement and they have just greenlighted the abuse that’s been going on on social media.”

Asked whether Arnold should consider his position at United, Riley said: “Yes, yes I do.”