Radu Dragusin is due to see a knee specialist on Monday, when Tottenham will learn the full extent of the injury he suffered against Elfsborg last week.
Ange Postecoglou has admitted “it doesn't look good” for Dragusin and Spurs fear the Romania centre-back will miss most of the rest of the season.
Losing Dragusin for an extended period would be another blow for Spurs, who are trying to sign another defender on deadline day following their £20.9million signing of Kevin Danso.
Spurs have just got Micky van de Ven back from his latest hamstring injury but Cristian Romero remains sidelined.
Ben Davies and Archie Gray were brilliant in Sunday’s 2-0 win over Brentford but Postecoglou has admitted Spurs have been left “a little bit thin” in defence.
“With Radu, we'll probably have more information [on Monday],” said Postecoglou.
“It doesn't look good, but I think he's seeing specialists tomorrow and we'll have more information then.”
Asked about the deadline-day search for another new centre-back, Postecoglou said: “It's about seeing where we're at in terms of the fit of the player.
“It's not just about bringing another body in, I've said that all along. We're still a little bit thin defensively.
“It goes under the radar, but the job Archie Gray's doing is just ridiculous. 18 years old, he's never played centre-back before, he's playing in the Premier League, and Europe midweek, every game. It's just incredible, that's he's churning it out. And Ben's been brilliant.
“But really at the moment, Micky we've got to be careful with, obviously, because he's been out for a while. Getting him back's great. Cristian, we feel, still a little bit away. Again, if the right opportunity exists, we'll go for it.”
