Newcastle striker Papiss Cisse has issued an apology in relation to the alleged spitting incident between himself and Manchester United defender Jonny Evans on Wednesday.
The Football Association is to launch an investigation into the incident during United's 1-0 away win at St James' Park, as disciplinary chiefs are awaiting match referee Anthony Taylor's report while at the same time reviewing video footage, according to Press Association Sport.
The pair clashed after an Evans challenge on Cisse, with television replays suggesting both men had spat during an ugly confrontation.
Under disciplinary rules, the players could face a six-game ban if the FA takes action over the incident.
Evans released a statement on Thursday afternoon denying spitting at Cisse, while the striker released his own statement soon afterwards.
Cisse said via the club's official website: "I have apologies to make to a lot of people today. Firstly to my teammates and to our supporters, secondly to Jonny Evans, and thirdly to every football fan who saw the incident between myself and Jonny.
"I reacted to something I found very unpleasant. Sometimes it is hard not to react, particularly in the heat of the moment. I have always tried hard to be a positive a role model, especially for our young fans, and yesterday I let you down.
"I hope children out there playing football for their clubs and schools this weekend will know better than to retaliate when they are angry. Perhaps when they see the problem it now causes me and my team they will be able to learn from my mistake, not copy it."
Evans said earlier on Thursday afternoon: "Having woken up this morning I am shocked to have seen the media coverage from last night's match. I would like to make it clear that I did not spit at Papiss Cisse.
"I was totally unaware of any spitting incident and had assumed that the issue at the time was with the challenge and his attempted retaliation to the tackle from the floor.
"During the game Papiss Cisse and I spoke about the incident and it is clear by my reaction in the television footage that I was totally surprised by any suggestion of spitting.
"It is not in my character or in my nature to spit at anybody nor is it something I have ever done or would ever do. It is certainly not something that I did last night."
Referee Taylor is unlikely to have seen the confrontation as he followed play after waving away Cisse's initial appeals for a free kick, although he was quick to intervene as tempers frayed once his attention was drawn to the fracas.
Both United boss Louis van Gaal and Newcastle head coach John Carver admitted they had not seen it in the immediate aftermath of the game, and the Dutchman said he could not imagine Evans spitting at an opponent.
George Boyd served a three-match suspension last season for spitting at Manchester City goalkeeper Joe Hart, a charge the then Hull player denied.
A similar sanction could prove costly for both clubs, with United facing Arsenal in the FA Cup quarterfinals and Premier League top-four rivals Tottenham and Liverpool in the next few weeks, while Cisse is Newcastle's leading goalscorer on 11 for the season.
Information from the Press Association was used in this report.