Maddison made an immediate impact when he joined the North Londoners from relegated Leicester City last June but the England midfielder has been out since November with an ankle injury.
"He's trained all week and he is fine. He is available and ready to start," Postecoglou told reporters.
"When someone is available I assume they are ready to start. Whether they do or not depends on what I see with everyone else tomorrow and I usually make those decisions game day.
"The beauty of it is he's got through the week really well and ready to go."
Postecoglou said Dejan Kulusevski was also fit after missing the 2-2 league draw with Manchester United at Old Trafford last Sunday. Spurs remain without South Korean captain Son Heung-min and midfielders Yves Bissouma and Pape Matar Sarr, all on international duty.
Tottenham go into the match with their players refreshed after a four-day break.
"We’ve had a really good training week. It helps when the numbers are up. Your training's just a little bit more intense, there’s that bit more quality there, which helps the whole group," said Postecoglou.
"I think it has been beneficial but obviously we've got three games coming up which will test our preparations."
The Australian said injuries and absences had made it a difficult period for the club for quite a while but the players had come through it well.
"We've set ourselves up now for hopefully a strong finish to the league season and a good cup run," he said.
