The Czech Republic goalkeeper has been linked with a move away this summer.
But ahead of tonight's Super Cup against PSG, Frank said: "He's a very good goalkeeper, very pleased with him. We are privileged to have three good goalkeepers in (Guglielmo) Vicario, Antonin and Brandon (Austin).
"There was good competition last year. Clearly we need good keepers in the squad. Antonin in my opinion has a great future ahead of him and he is clearly a Tottenham player this season."
Meanwhile, Frank was also asked about Tottenham competing with Arsenal for the signing of Crystal Palace attacker Ebere Eze.
He replied: "There are a lot of good players out there, there are also a few from the PSG team but I don't think we can buy them right now. In general, players in and players out, I'm only speaking if something is done or not done. I speak only about my own players."