Corluka joined Bayer Leverkusen on-loan in January.
"Tottenham, for me, had one of the best teams in England and of course it will be an unsuccessful season if they don't go to the Champions League," the defender said.
"I don't know what the chairman will do if they don't qualify. I know only that it will be an unsuccessful season.
"Three months before they were in the title race challenging [Manchester] City and [Manchester] United.
"Now they are three points behind fourth spot. They are fifth and it's going to be really difficult for them."