Lions lock Danny Grewcock has been banned for two months after being found guilty of biting New Zealand hooker Keven Mealamu during the first Test.
Grewcock came on for Ben Kay after 57 minutes of Saturday's 21-3 defeat and afterwards was reported by independent citing commissioner Willem Venter.
He is now out of the tour after being banned following a lengthy disciplinary hearing on Sunday that lasted all day.
The Lions will announce on Monday if they are to call up a replacement.
"The judicial officer accepted that Mealamu's fingers inadvertently entered Grewcock's mouth at the breakdown," said an International Rugby Board statement.
"But rather than removing the fingers in a more conventional way, Grewcock bit Mealamu's right ring finger, and accordingly he found that the player was guilty of biting."
Afterwards Grewcock expressed disappointment with the decision.
"I do not agree with the decision, because as I argued to the hearing, I did not bite the player at all," he said.
"But I have to accept the decision and that means for me the tour is over. I have decided therefore that I will return home as soon as I can.
"I think that is the best course of action for me, and for the tour. I now hope that the rest of the Lions squad go on to win the next two Tests.
"I'm just sad that they will have to do it without me, and wish them all the very best for the remaining matches on the tour."
Head coach Sir Clive Woodward, who could call up Wales lock Brent Cockbain, said that he had no problem with the decision.
"Part of me was quite pleased that he was cited because it takes the matter out of your hands," he told Radio Five Live.
"I have not seen what Danny has done as I have been concentrating on the Brian O'Driscoll injury.
"Obviously they have banned him for two months and I have to say that it is the right decision. That is why the process is in place and clearly he has done something wrong."
It is latest in a line of disciplinary problems for Grewcock, who was sent off playing for England against New Zealand in 1998 as well as being banned last summer after being cited for reckless use of the boot.
The Bath forward is banned from playing until 26 August.
It is a further blow for Woodward, who lost captain Brian O'Driscoll, Richard Hill and Tom Shanklin from the tour on Saturday.
O'Driscoll dislocated his shoulder after being tackled by both Mealamu and All Blacks skipper Tana Umaga.
The Lions made an official complaint to Venter but the South African said that the pair have no case to answer.