Klaassen proved to be an instrumental figure for the Dutch outfit last term, as Ajax progressed into the final of the European competition before losing out to Jose Mourinho's Manchester United.
"You need a lot of players because the season will be long and there will be a lot of matches," said Klaassen, according to the Liverpool Echo.
"We had that at Ajax last year, a lot of matches. You can't have 15 or 16 players - you need 20 or 25.
"I played a lot of matches in the competition last season and hopefully I can go that far this season with Everton as well."
Klaassen joined the Toffees for £26.3m earlier in the summer as part of Ronald Koeman's recruitment drive.