Leicester defender Ricardo Pereira will be out of action for up to six month following Achilles surgery, Foxes manager Brendan Rodgers said on Friday.
Portugal right-back Pereira had an operation on Thursday after suffering the injury during last week's friendly win against Sevilla.
Rodgers added Harvey Barnes will miss Sunday's Premier League opener at home to Brentford.
"It was looking really good, but we've picked up injuries against Sevilla," Rodgers told a news conference on Friday.
"Sadly Ricardo Pereira will be out for up to six months with a ruptured Achilles. A lot of our game idea was about our full-backs and him in particular. He was looking so good.
"It's a massive blow to him. He had his operation last night and he'll recover now, get strong again and come back better I'm sure."
This is, however, yet another setback since Pereira joined Leicester from Nice in 2018, with the player sidelined for nine months after damaging knee ligaments in March 2020.
Rodgers said winger Barnes could be out for "a few weeks" due to a knee injury.
"Hopefully he won't be too long and he can come back and pick up where he left off," the manager said.
Leicester are the only Premier League club yet to make a pre-season signing and Rodgers, who has seen long-serving goalkeeper Kasper Schmeichel join Nice, and Rodgers is not expecting any new arrivals.
"As things stand, I believe not," he said.
"I mentioned that before, there's nobody imminent coming in. The concentration has purely been on the players who are here. I think we can do well."
The Northern Irishman added: "I felt this was a time we would need to improve, but I respect the club's position. The club have been outstanding in supporting me. This time, I need to support them.
"It's unfortunate. I don't need to fight with anyone. I would have loved to improve the squad and there is time until the end of August if things change.