Benitez is set to leave the club at the end of the season following his interim appointment after the removal of Roberto Di Matteo. Chelsea won the Europa League earlier this week, and look set to clinch a Champions League qualification spot.
And Benitez believes Chelsea owner Roman Abramovich will fund a title push next season by spending up to €100m in the summer transfer window.
Speaking to Spanish radio station Onda Cero after the Europa League final in Amsterdam, Benitez said: "Chelsea will be much better next season because they will spend €100m and they will sign three of four players.
"The foundation is already there. The future is bright for them.
"I don't know who the next coach will be, I am not the person who should say, but everyone speculates the same person."
Real Madrid boss Jose Mourinho is the manager most commonly linked with the soon to be vacant post at Stamford Bridge.
And the ex-Chelsea boss would have a strong squad to work with next season, boasting an impressive blend of youth and experience.
Abramovich financed a summer spending spree last summer, splashing out close to £75m on Victor Moses, Oscar, Cesar Azpilicueta and Eden Hazard.
With a season under their belts, these young stars will be expected to kick on next term, and if Chelsea do add "three or four" new players they could mount a serious challenge to the two Manchester clubs.
A new striker is widely regarded to be the priority, with Atletico Madrid striker Radamel Falcao and Napoli forward Edinson Cavani believed to be two of the top targets.