Tottenham forward Heung-Min Son could be sidelined for at least "a few weeks" with a foot injury and is out of his side's Europa League clash with Monaco on Thursday.
The 23-year-old South Korean suffered a muscle injury in his foot during Saturday's 4-1 victory over Manchester City and is to be assessed on a day-by-day basis in order to determine when he can return.
Son did not travel with the squad to Monaco on Wednesday evening - and neither did fellow injured players Ryan Mason, Nabil Bentaleb, Mousa Dembele or Alex Pritchard.
Pochettino told Sky Sports News HQ: "It is bad news about Son - he got a foot injury against Manchester City and we need to assess him for the next few weeks.
"We hope it's not a big issue but he has a problem in his foot and we need to assess it day-by-day, but maybe he will be out for a few weeks.
"There are still some injuries to players such as Alex Pritchard, Nabil Bentaleb and Mousa Dembele too. Ryan Mason is close but is still out, but maybe after the international break he will join the group again."
Son's injury paves the way for fellow new signing Clinton N'Jie to make his first Tottenham start, as Pochettino admits there will be changes to the side that shocked City at White Hart Lane.
He said: "Maybe he has the possibility to play but first we need to analyse the team and try to pick the best player to win the game.
"We need to keep the momentum. The mentality in the team is what is important and maybe there will be some changes but not too much."
Earlier on Wedneday, the North London club confirmed on their website: "Son sustained a foot injury in a challenge during Saturday's win v Man City and has spent the past few days being reviewed.
"Our medical staff will monitor Son's progress during his rehabilitation in order to determine when he will be fit to return to training."