David Wagner said Terence Kongolo sustained a serious hamstring injury during Huddersfield Town's Premier League loss to Tottenham.
Huddersfield are bottom of the table and still yet to score a home goal in the league this season after Harry Kane's brace in a 2-0 Spurs win on Saturday.
Kongolo left the field on a stretcher during the first half, the centre-back having seemingly injured himself in the process of trying to stop Spurs' opening goal.
The club's record signing could be out for an extended period and Huddersfield will also assess Kongolo's fellow defender Christopher Schindler over a knee injury.
"My biggest concern is with Terence Kongolo," Wagner told a news conference.
"It looks like a serious hamstring injury from a stretch.
"Christopher Schindler had a twist and it was too painful to play on.
"There was no fluid on the knee, but we need to make further investigations."
Wagner felt decisions went against his side against Spurs, who doubled their lead from the penalty spot after Kongolo's replacement Florent Hadergjonaj was adjudged to have brought down Danny Rose.
The Town boss highlighted an apparent foul on Chris Lowe that went unpunished in the first half when the score was goalless as he bemoaned Huddersfield's lack of luck.
"The penalty which we conceded was a soft one," Wagner added.
"I think there was a clear foul on Lowe in the first half. We can discuss whether it was in the box, but it was a clear foul.
"Everybody who has seen this game can see that my team performed on a very good level. The atmosphere and stats speak for themselves this week.
"If you perform consistently, as we have done in recent weeks, the reward will come. This is what we should be focused on.
"It is a results-driven business, but for me as a manager it makes more sense to focus on recent performances."
