Merseyside police are reviewing CCTV footage to establish if Manchester United forward Cristiano Ronaldo committed an offence by knocking a mobile phone out of a supporter's hand following his side's 1-0 Premier League defeat to Everton on Saturday.
Footage emerged on social media of Ronaldo appearing to swipe his hand towards the ground as he walked off the pitch and headed for the tunnel at Goodison Park. Eyewitnesses said the 37-year-old had knocked a fan's phone out of their hand and it smashed to the ground.
- Dawson: Everton loss suggests United not good enough for top four
- De Gea questions United after 'unacceptable' defeat
Ronaldo took to Instagram to apologise for the incident.
"It's never easy to deal with emotions in difficult moments such as the one we are facing," Ronaldo said. "Nevertheless, we always have to be respectful, patient and set the example for all the youngsters who love the beautiful game.
"I would like to apologise for my outburst and, if possible, I would like to invite this supporter to watch a game at Old Trafford as a sign of fair-play and sportsmanship."
United told ESPN they are investigating the incident.
A spokesperson for Merseyside Police said the force was liaising with both clubs after reports of an alleged assault.
"As players were leaving the pitch at 2.30 p.m., it was reported that a boy was assaulted by one of the away team as they left the pitch," the spokesperson said.
"Inquiries are under way and officers are working with Everton Football Club to review CCTV footage and are carrying out extensive witness enquiries to establish if an offence has taken place."
Ronaldo, United's top scorer this season, returned to the United team after missing last weekend's 1-1 draw with Leicester City due to illness.
However, he was unable to inspire the team to victory against relegation-threatened Everton.
The defeat left United seventh in the Premier League standings and they face the prospect of missing out on qualification for next season's Champions League as they are six points adrift of fourth-placed Tottenham Hotspur.