St Mirren are still waiting to hear the extent of Darren McGregor's knee injury but expect the defender to be out of action for up to nine months.
The 25-year-old came off against Dundee United last weekend after what he himself described as an innocuous challenge from Gary Mackay-Steven.
And manager Danny Lennon said: "He definitely has cruciate damage, but we don't know the full extent as yet.
"But we are talking of Darren being out of action for six to nine months."
Lennon on Friday brought in former Telstar central defender Illias Haddad as a replacement in the expectation that McGregor will miss the bulk of the season.
But the manager is still hopeful that McGregor will make a faster than expected recovery.
"Darren has been moving around with the aid of crutches and the swelling on his injury has gone down," Lennon told his club website.
"He'll go through his operation on 1 September.
"We're hoping that, with the medical staff that we have here at the club, we will get towards the lower end of the scale in that time-frame.
"The determination and the work-rate of Darren, along with his hunger and character, will hopefully aid towards that lower end of the time-scale.
"But we'll know a lot more once the operation has been done."