Newcastle boss Steve Bruce says Hamza Choudhury's "horror" tackle could have ended Matt Ritchie's career.
Ritchie, 29, is facing two months out after the challenge by the Leicester midfielder in Wednesday's Carabao Cup second-round game left him with ankle ligament damage.
"It could have been eight months, it could have been career-ending," said Bruce.
"If his leg had been planted on the floor, he was in serious trouble."
Leicester boss Brendan Rodgers has defended Choudhury, who on Friday extended his contract at the Foxes until 2023.
"I spoke to Steve after the game. It's one of those challenges, it's very committed," Rodgers said.
"He's a real genuine, honest boy, Hamza, so he certainly wasn't looking to injure anybody.
"He wouldn't go in on purpose. He's a very strong player, a very honest player and we don't ever want to lose that from him. He understands it's a part of the game he needs to focus on."
In June, 21-year-old Choudhury apologised for an "over aggressive" tackle on Jonathan Bamba during England's European Under-21 Championship defeat by France.
Choudhury was sent off and Bamba went to hospital for X-rays.
Ritchie, usually a winger, has operated as a left wing-back this season, starting Newcastle's three Premier League games.
Jetro Willems, a possible replacement, is doubtful for Saturday's home game against Watford.
Paul Dummett is another option for Bruce, who claimed his first win since taking charge at Tottenham last weekend.