Mauricio Pochettino's Spurs, who lost the league title to Leicester City and finished third last campaign, trail leaders Chelsea by four points with six games to play this season.
"Tottenham are a really great power in English football, they are working for three years," Conte told the media on Friday.
"They are a great team, they are showing for the second year to fight for the title. Last year they missed this, they are doing it again and are full of great, strong players.
"They are building something important. There is a moment you have to finish to be considered underdogs, this is the moment."
Chelsea goalkeeper Thibaut Courtois will return for the Wembley clash after missing the 2-0 league defeat at Manchester United last weekend, but Gary Cahill could miss out after being taken to hospital earlier this.
"When we started to have the training on Tuesday, he arrived with a bit of fever," Conte added. "Our doctor preferred to take him to hospital, it is not a serious problem.
"He is getting better, he is improving a lot. For tomorrow, it is very difficult."
Read the full article on eurosport.co.uk: Spurs no longer the underdogs, says Chelsea's Conte