Defenders Micky van de Ven and Ryan Sessegnon are also out injured, while full-back Destiny Udogie is suspended for Thursday's match at Brighton.

"[It's] disappointing to lose [Romero], for sure," said Postecoglou.

"He had a scan the other day and has got a hamstring strain. We are looking at probably four or five weeks for him."

World Cup winner Romero missed three matches through suspension in November and December after being sent off in Tottenham's 4-1 home defeat to Chelsea.

They picked up just one point in the centre-half's absence and lost to West Ham on his return, but have since won their past three matches.

Spurs are fourth in the Premier League, six points behind leaders Liverpool, who have played one game more.

"We obviously missed him with the suspension and now we've just got him back and he steadied things up," Postecoglou said.

"Now he will be missing again for quite a chunk of time."

Netherlands defender Van de Ven had built up a promising partnership with Romero before he injured his hamstring against Chelsea in November.

Postecoglou says Van de Ven is "getting closer" to a return to first-team training, but believes the 22-year-old centre-back will not be ready until the Premier League match at Manchester United on 14 January.

"He is at the tail end of it, for sure," added Postecoglou. "At some point, middle of January, he could be available, but how we use him after such a long absence will be depending on where he is at."