The Portuguese confirmed that the 32-year-old has undergone surgery.
Sheffield Wednesday's Glenn Loovens
The 32-year-old had an operation on his ankle on Wednesday, the Sheffield Star reports, and the Portuguese explained that he is now set to miss the opening weeks of the campaign as he recovers.
Sheffield Wednesday manager Carlos Carvalhal
"It is, of course, not good news for us because Glenn is the captain of the team and an important player," he told the Star.
"It is a small problem that he felt last season.
"It is a surgery so he will be out a minimum of six to eight weeks."
The news that the centre-back is set to be stuck on the sidelines will be a major blow to the Owls' chances of getting off to the fast start that eluded them last year.
Even if the Dutchman is back after six weeks, he will have still missed the clashes with recently-relegated pair Aston Villa and Norwich, as well as the Yorkshire derby against Leeds and the potentially-tricky trip to face Burton Albion.
While there is still a long way to go in the summer, Wednesday may also be concerned about the lack of options they currently boast in defence. Of their current squad, only Tom Lees, Jack Hunt and Liam Palmer also played regularly last season, so they would have surely been relying on Loovens to be a key man once again.