Chelsea striker Diego Costa was sent off in Saturday's FA Cup defeat after placing his head and mouth on the neck of Everton's Gareth Barry.
After the game, Chelsea interim manager Guus Hiddink said he could not be sure certain if Costa bit Barry while the two came face-to-face with six minutes remaining.
The incident was just the latest in a series of controversial moments surrounding Costa this season, and meant more misery for Chelsea, whose last hopes of winning a trophy this season ended in the 2-0 loss.
In the first half, Costa had earned a yellow card after a clash with Barry, and he then appeared to spit at the feet of referee Michael Oliver.
Costa was later sent off in the 84th minute after objecting to Barry's challenge, which sent him sprawling to the pitch.
The striker quickly rose to his feet and made contact with Barry with a chest bump, then pushed his head into his opponent's face before lowering his open mouth to the Everton man's neck.
Barry did not pull away, and Costa pulled his opponent in for a brief embrace before they were separated.
Oliver then dismissed Costa while also booking Barry, who was himself sent off after another tackle three minutes later.
There was immediate debate as to whether Costa had bitten Barry during their confrontation.
Hiddink said he didn't see a bite but said he'd wait to make up his mind on the incident.
"I always try to be fair in my judgement, pro or con. I haven't seen it so it's difficult for me to say yes or no," said Hiddink, who said he had yet to speak to his striker.
"He was chased a bit in the game as well. They went after him. They knew it and it's within the rules, but also as a referee you must protect a bit the situation, knowing and feeling the atmosphere when there are a multitude of little provocations."
Everton manager Roberto Martinez downplayed the incident after the game, preferring to focus on his side's win.
"My interpretation is that I don't think it was a key moment in the game," Martinez said. "I don't think we should focus on that. It was an emotional game and rightly so -- you want to see players desperate to win the game for your team. Diego Costa had a fighting spirit.
"I would like to praise the referee for the way he handled those emotions. The sending off of Costa was right, the sending off of Barry was right. He never allowed those emotions to stop the fluency of the game, and that's what you want.
"Whatever happened with Costa, I think we should see it as a good game with real emotion."
Martinez also said Barry did not report anything to him after his clash with Costa.
"We won a game against Chelsea two-nil, we just went into a semifinal," Martinez said. "As a manager the last thing I'm going to do is see if an opposing player has bitten my player. I'm not interested.
"Gareth Barry said nothing to me so I'm not worried -- I'm just disappointed that he collected the second yellow card."
Asked about Hiddink saying his players "chased" Costa during the game, Martinez said: "You can interpret as you want.
"My interpretation was two teams that matched each other well. None of my players fell into the game of losing their focus. We went through an incredible pain, an undeserved pain last week [against West Ham] and I really enjoyed our focus.
"Anything else that you can look into the opponent's reactions, I'm not really interested."
Former Liverpool and England striker Robbie Fowler wrote on Twitter:
I'm a fan of Costa tbf.... But he deffo thought about a bite there...
- Robbie Fowler (@Robbie9Fowler) March 12, 2016
Former United States international Stuart Holden wrote that he believed Costa had bitten Barry, referencing Luis Suarez's infamous bite of Italy's Giorgio Chiellini in the 2014 World Cup.
All Revealed... Costa.. Cousin of Suarez. Nice chomp on Barry there
- Stuart Holden (@stuholden) March 12, 2016
Costa made headlines earlier this season for after being charged with violent conduct for his actions against Arsenal. He was suspended for three games.
In September, the Spain international clashed with Laurent Koscielny, raking his hands across the Arsenal player's face and then chest-bumping him to the ground.
Gabriel Paulista then came over to defend his teammate, and he and Costa both received yellow cards following their confrontation. But a minute later the Arsenal centre-back was sent off for flicking a boot at Costa.
Hiddink laughed off suggestions that Costa needed to go to anger management, while also defending his player's intensity.
"There is a movie about that, I think... with Jack Nicholson. I've seen the film," Hiddink said. Maybe we'll go and watch it together.
"I like that he goes on the edge. He desperately wanted to play today. It would have been better to rest but this isn't the type of game where you rest players. You like to have all the big players on board.
"It's a combination of not total physical fitness and small provocations, but he has to take responsibility for himself in this incident."
Suarez's habit of using his teeth come to a head when he was charged with biting Chiellini at the World Cup. The Barcelona forward was banned from competitive matches for four months as well as the next nine international games for Uruguay.
Information from ESPN FC's Chelsea correspondent Liam Twomey was used in this report.