Israel midfielder Beram Kayal will miss the first two months of Brighton's Premier League campaign after suffering a broken leg.
The 29-year-old suffered a broken fibula in Brighton's 3-2 home friendly loss to Atletico Madrid on Sunday.
Seagulls boss Chris Hughton expects the former Maccabi Haifa and Celtic star to be sidelined for at least eight weeks.
Kayal underwent successful surgery to correct the problem on Wednesday, but the eighth major operation of his career now denies him the chance to feature at the start of the campaign.
"We had some bad news on Beram Kayal who came off at half-time in Sunday's game," said Brighton manager Hughton.
"He's got a small break in his fibula, which was operated on today, and we expect him to be out for a period of something like eight to 10 weeks.
"The good news is it was a clean injury as such.
"The operation went very, very well. We don't expect any complications, but it's bad news for us and for him."
Sam Baldock will miss Saturday's league opener when Brighton host Manchester City, with the striker still recovering from calf surgery.
But Anthony Knockaert will be available to boss Hughton, after shaking off ankle ligament damage.
"Sam Baldock had surgery on his calf in the summer, and that's just the process of time really," said Hughton.
"He's back into part training, but we're still expecting him to be out for a little while.
"He had to rest for a good period in the summer so everything was later.
"So we still expect that to be a little longer with Sam.
"Anthony (Knockaert) is fine, he played part of a game yesterday behind closed doors.
"So he's fit and up and running."
Brighton's clear aim on their maiden Premier League season will be to avoid relegation.
But Hughton insisted he has set no hard and fast targets with his players ahead of the weekend's daunting league opener against City at the Amex Stadium.
"We haven't set any targets," said Hughton.
"The outcome we'd like this season is to have a go, and to make sure that our first season in the Premier League we give it the best we can, that we have a real good go, and that we can have no complaints at the end of the season that we didn't do enough."