The midfielder sustained an ankle injury in the 2-1 home defeat to Udinese prior to the squad flying out to Austria for this week's training camp.
Although the 28-year-old travelled out with the rest of the squad, he has been forced to sit out both pre-season friendly games while abroad.
And head coach David Wagner has exclusively revealed to the Examiner the injury is worse than initially thought with the player potentially missing the opening month of the club's inaugural Premier League campaign.
“We hope he will be back on the pitch with the medical department at the end of next week,” said David Wagner after watching his side's 2-2 draw with Italian side Torino.
“If he progresses quickly he may be able to help us before the international break and we will be very happy.
“If not, then I am sure he will be back at some point after the international break.”
The German head coach also went on to say Martin Cranie's hip injury is likely to see the right-back ruled out for between six to eight weeks.
And that could leave the door open for Dimitri Cavaré to earn a deal at the club after spending the last few weeks on trial at the club.
Although featuring in the draw against Stuttgart, the 22-year-old returned home after experiencing some tightness in his legs after the game.
“We will make a decision on him over the weekend,” revealed Wagner.
“I think his trial was good and now we will negotiate with him and Rennes to see if we can come to some sort of arrangement.”