The incident is alleged to have taken place during a ruck in the 64th minute of the 27-9 loss at Cape Town Stadium.
Sinckler, who has a chequered disciplinary record, will be hit with a minimum 12-week ban if the citing is upheld by Tuesday’s disciplinary hearing.
Remarkably, no other player has been cited from a fractious clash despite numerous flashpoints.
Earlier in the day the Lions issued a statement on behalf of Stuart Hogg in which the Scotland full-back denied his own biting incident involving opposite number Willie Le Roux.
Hogg’s head made contact with the left arm of Le Roux when tempers flared in the second half with footage and stills of the incident going viral on social media, but he has been cleared of wrongdoing.
“Following speculation that has surfaced online, I would like to categorically deny any foul play in last night’s game,” Hogg said in the statement.
“I would never bite an opponent and I am annoyed and upset by this unsubstantiated accusation. I’ve always been proud of playing rugby in the spirit of the game.
“Respect to the Springboks for their deserved win yesterday. The squad is hurting after last night’s defeat, but it’s all to play for next week. It’s going to be a cup final and everyone’s going to be up for it.”
However, Sinckler now faces an anxious wait knowing biting is treated severely by rugby’s judiciary and carries a low-end sanction of a 12-week ban, rising to in-excess of 24 weeks for severe offences. The maximum length of suspension is 208 weeks.
The England prop, who was a second-half replacement for Tadhg Furlong, can expect little mitigation if the biting incident is proven because of his previous misdemeanours.
In January he was suspended for two weeks for swearing at a referee and four years ago he received a seven-week ban for gouging.
A bad-tempered collision turned into a savage grudge match and it is surprising more players were not cited, the requirement for which is that an offence is worthy of a red card.
A clip of Maro Itoje resting his knee on the throat area of Damian De Allende has also been widely viewed on social media.
As Itoje rises to his feet, the protesting De Allende tackles him to floor and then shapes to throw a punch downwards at the prone Lions second-row, who was man of the match in the first Test.
South Africa made their own contribution to a stormy evening.
Cheslin Kolbe was fortunate to be punished with only a yellow card for taking Conor Murray out in the air and the Springbok wing also clattered into Tom Curry with a clumsy head-first tackle that the officials dismissed.
And referee Ben O’Keeffe also brushed over another potentially dangerous challenge by Faf De Klerk, who connected high with the hapless Murray.
Putting to one side the disciplinary fallout from the penultimate match of the tour, coach Warren Gatland must pick his Lions up from their heaviest defeat since the disastrous 2005 visit to New Zealand.
The Lions toiled up front and their back three were vulnerable to the aerial bombardment they knew was coming, so changes appear inevitable.
“We’ll spend the next couple of days reviewing the game and then looking at what we think is the best 23 to put out,” Gatland said.
“Whether that’s some fresh faces who haven’t been involved in the first two games…we have got lots of options to give us energy and perhaps some momentum as well.
“Or do we put out that same team and give them the chance to redeem themselves? Those are the conversations we’ll have over the next couple of days.”