England captain Owen Farrell was sent off as his side came from behind to beat Wales 19-17 in a scrappy Rugby World Cup warm-up match at Twickenham on Saturday.
The flyhalf was initially shown a yellow card for a high tackle to the head of Wales replacement Taine Basham in the final quarter.
But under new rules that allow a review panel to consider an act of foul play while the game is in progress, that was soon upgraded to a red.
When Farrell left the field on Saturday, it meant a lacklustre England, who kicked off close to full strength, were down to 12 men with replacement prop Ellis Genge and full-back Freddie Steward having been shown yellow cards as well.
But England overhauled a 17-9 deficit thanks to Maro Itoje's converted try from a driving maul and a late penalty from replacement George Ford as they avoided a fourth successive defeat and a slump to ninth in the world rankings.
The worry now for England, who have two more warm-up games, against Ireland and Fiji, is that any ban for Farrell could rule their talisman Farrell out of the start of the World Cup, with Steve Borthwick's team launching their Pool D campaign against Argentina in Marseille on 9 September.
Farrell's three-match ban for a similar offence in January could now count against him in any disciplinary hearing.
Adding to England's concerns was the ankle injury suffered by scrumhalf Jack van Poortvliet, with the Wales trio of captain Dewi Lake, Taine Plumtree and Basham all going off injured as well.
"Regarding Owen, we'll wait and see what happens," England coach Steve Borthwick told Amazon Prime.
"The same with Jack van Poortvliet, he'll get a scan. Rather than jump to any conclusions, we'll wait and see what happens.
"As this builds, I want to make sure we've got fundamentals in place. Our set piece, our kicking game and defence were in a strong position. The attack is the final building block and takes the longest to come, but that's what we're working on."
