France international Sissoko, 27, did not even make the bench for Spurs' 2-1 defeat at Chelsea on Saturday.
"Football is not about money," said Pochettino.
"You need to show on the training ground you are better than another team-mate and you deserve to be involved."
Sissoko joined Spurs on a five-year contract after they matched Everton's bid on transfer deadline day in September.
He has made five starts in all competitions, plus five more appearances as a substitute.
However, he has not played in the Premier League since being given a three-match ban for elbowing Bournemouth's Harry Arter on 22 October.
The former Toulouse player missed the EFL Cup tie against Liverpool as well as league games against Leicester and Arsenal, but was not involved against West Ham on 19 November.
"If you sign a player and you expect something and you do not find what you expect and if another deserves to be involved, like (Georges-Kevin) Nkoudou or (Vincent) Janssen - why? Because we paid money we need to put the player to play?" added Argentine Pochettino.
"Of course he needs to work hard and show in the future he deserves to be involved in the team.
"I need to take a decision and I believe the players that start on the bench deserve to be involved."
Tottenham midfielder Moussa Sissoko has failed to live up to expectations following his £30m move from Newcastle, says manager Mauricio Pochettino.