Police are investigating claims of a racially-aggravated assault at Manchester United’s football stadium, after a 19-year-old who used to play for the club’s youth development team said he was attacked by security guards and left with a fractured eye socket as he tried to get to his job at the ground.

Greater Manchester police confirmed on Tuesday that they were looking into a report of a public order offence and assault by two men at Old Trafford on 27 February.

Alleged victim Kamarl Nelson, who had also been a ball boy for the club and will go to university to study football science later this year, was on his way to work on a cleaning shift when the incident happened. The community interest company Kids of Colour said that he had been called “a slave” before being slammed against a wall and hit in the stomach by guards who disputed that he worked at the stadium.

Kamarl Nelson, 19. Photograph: Supplied

Controlled Solutions Group (CSG), which is contracted to run security operations for Manchester United, has strenuously denied the allegations against its employees.

In a post on Twitter, Kids of Colour said guards had not believed Nelson worked at the stadium, despite him arriving in a uniform with Manchester United labels and having worked there for six months.

They also claimed that a guard said he was “surprised I didn’t find a knife” to the teenager after searching his bag.

Nelson told the Guardian that he was “shocked” at CSG’s denial and said that the incident should be investigated because “if this isn’t brought to the attention of the police then the same thing will just occur again”.

In a text message he went on: “There are plenty of incidents similar to mine which men and women of colour have to endure but are just swept aside, which I don’t believe is right. This can show if you do endure these circumstances you are able to speak up.”

His mother told the Guardian that their family had been “deeply impacted” by the incident, and wanted “all those involved to be brought to justice”.

Kids of Colour said that on 28 February, the 19-year-old attended Trafford General hospital, where he was informed he had bruised ribs and a fractured eye socket.

Nelson is an outsourced contractor at the stadium, employed by the events staff recruitment agency Arc. A representative for Arc said the incident was being handled by police but would not confirm any details.

At 15, the teenager was mentored by a coach with the Manchester United Foundation. He was pictured in a brochure, where he said working with the club’s charitable arm had helped him “not just progress as a player but as a person”.

Kids of Colour said Nelson had explained to guards that he had no proof he worked at the stadium because pass cards and badges are not allowed to be taken home, as they can be used at other venues.

The community interest company claimed he asked guards to speak to his manager over the phone but they refused, before threatening him with physical violence if he did not leave the premises.

The Twitter post alleges that Nelson was assaulted as he tried to hold on to his bike. After the bike was thrown across the street, he was slammed against a wall and then hit repeatedly. Arriving police officers then told the teenager that he “didn’t need to be so angry”, the statement alleged.

A statement from GMP said: “Shortly before 8pm on Thursday 27 February 2020 it was reported that two men subjected a man to racist comments before assaulting him.

“An account was taken from the victim later that evening and officers have since been keeping in contact with him while working to gather further important information.”

The force said CCTV footage from the area where the incident is believed to have taken place was being examined to try to determine those involved.

A spokesperson for the CSG said: “CSG will be fully compliant in support of any police or other investigation into these false allegations.”

A spokesperson for Manchester United said: “We are aware of an alleged serious incident prior to the Club Brugge match on 27 February. We are cooperating fully with the police and await an outcome from their investigation.”