Sheffield Wednesday physio Mark Palmer expects striker Francis Jeffers to be sidelined for four months.
The former Blackburn, Arsenal and Everton forward was stretchered off during the 4-2 win at Stoke after a challenge with Ryan Shawcross.
An initial assessment of the one-time England international's ankle suggested a break, however a scan has now revealed that Jeffers has suffered serious ligament damage of the ankle.
Palmer explained that the 26-year-old will now begin a lengthy rehabilitation period.
"With regards to Francis Jeffers he has been to see a surgeon over the last couple of weeks to have some scans and those scans confirmed that he has some serious ligament damage on both sides of the ankle which is a little bit unusual," he told the club's official website.
"We'll rehabilitate him conservatively for between six and eight weeks and then if Franny has tolerated that and his ankle seems stable then we can push on from there - we've put a time frame of approximately four months on Franny's return."
"It was difficult to see the exact problem initially and the X-rays were inconclusive because the ankle was so swollen - it was one of the most swollen ankles I've ever seen."