The Lilywhites ended the 2016-17 campaign as runners-up to Chelsea - their highest league finish in 54 years and their best-ever points tally.
Fowler believes that Spurs "got lucky", however, and has warned boss Mauricio Pochettino that he will have to spend big in the remaining weeks of the transfer window if he is to keep in touching distance of rival sides.
"They have been thereabouts the last two years and they have a quality manager who the players seem to rate, even rave about," he told The Mirror. "That makes them play for him, lifts them up a level and I think they have the basis of a squad that will be around the top four again. But they have actually made a couple of questionable signings in recent years.
"Moussa Sissoko was a rank bad buy, no question, but obviously that is with a hell of a lot of hindsight because he seemed to be the next superstar in the making. The Dutch lad Vincent Janssen hasn't cut it either, and he does not look Tottenham class. I am not slagging him, just being realistic – he is not good enough to replace Harry Kane. Spurs got lucky last season because [Harry] Kane only had one injury spell and they did not miss him too much.
"But if he gets a bad one or struggles, they will need better quality as back-up. They will go and spend. There will be a striker coming in – I've heard Bournemouth's Joshua King is a possible – and despite the fact there have been a few misfires in recent years, they have been building a good quality squad. But other teams will be stronger as well.
"City have spent the best part of £200m already, Chelsea will strengthen massively and United have spent £150m so far, with no sign of stopping. Arsenal have made a couple of decent-looking buys, too, Liverpool no doubt will and Everton are pushing with their impressive summer so far. So, if Spurs stay still in the transfer market, it could see them go backwards rapidly. That's the wonderful world of the Premier League these days – you may need to spend £200m to stay still."