New Preston signing Lee Trundle needs a knee operation that will keep him out of action for up to four months.
North End manager Graham Westley confirmed striker Trundle, 35, suffered ligament damage in a friendly defeat by Morecambe on 21 July.
"He was looking so good and working so hard," Westley told the club website.
"Lee is a strong character. He spreads a lot of positivity, although he has been a bit down with the news that he needs an operation."
Trundle, who signed a one-year deal at Preston after a successful trial, missed their 1-0 win over AEK Athens on Saturday.
Former Arsenal youngster Jeffrey Monakana scored a late winner for North End.