Vedran Corluka believes Tottenham could get left behind by their big-spending rivals next season if they fail to invest in the summer.
After bringing UEFA Champions League football to White Hart Lane for the first time last term, Spurs have missed out on a top-four finish this time around.
A Europa League spot is now the best they can hope for, with Manchester City or Arsenal battling to take the third and fourth Champions League spots.
And Croatia defender Corluka believes strengthening the squad during the off-season is key if Spurs want to push on.
"Some teams invested more money than us in players and this year we didn't make the cut," Corluka told Sky Sports News.
"We've showed in some games we can compete with them. But next season will be tough if we don't strengthen our team like they will."
Spurs enjoyed a strong maiden Champions League campaign, reaching the quarter-final stage before ultimately succumbing to Real Madrid.
Corluka admits missing out on competing in Europe's top club competition was tough to swallow after getting a taste of the action this year.
He added: "We are disappointed because we expected, after a season in the Champions League, to play in the Champions League again.
"We enjoyed it very much. Of course there's disappointment in the club and around the players as well but that's football. The Premier League is a tough league.
"Hopefully next year we will be in the top four again."