Spurs appear to have been beaten by Arsenal for Crystal Palace midfielder Ebere Eze in the latest of their high-profile transfer snubs over the summer.
For Sherwood, a former Tottenham manager, Frank is working with a squad short of quality and depth, which is a major concern given this season will include a Champions League campaign.
Asked if the Dane will prove a successful appointment, he told Tribalfootball.com: "Well, it all depends what you call success.
"I call success what Ange Postecoglou did last season, to be honest. I think that is success if you're a footballer or you're a football manager success is about winning and about lifting trophies. But it wasn't enough unfortunately. It wasn't enough for what the owners there at Tottenham wanted and decided to to change direction."
No riddles
On Frank's style, Sherwood continued: "I like Thomas Frank. I really do. I think he seems like really... I don't know him personally, but he looks like a really good man and talks a lot of sense. He doesn't speak in riddles, he actually gives it to you straight.
"I think he's got a decent group of players. But then again if he needs to win a trophy I think you need to recognise very early in the campaign which trophy he needs to target because obviously Ange Postecoglou decided, and I would suggest it was probably January time, that Tottenham weren't capable of winning on all fronts and competing on all fronts.
"So he put all these eggs in that Europa League basket, rolled the dice, and he'd come up with the right numbers and lifted a trophy and took Tottenham to the Champions League."
Disappointed for Ange
Sherwood also said of Frank's arrival from Brentford: "So a little bit disappointed that he lost his job on the back of that. But at the same time, I think it's a decent replacement. I really do. But only time will tell.
"If you ask Tottenham fans, what is success now? They're used to that open top bus now. It was not long ago. I mean, they've done it now. They've had the open top bus. So they'll want it again.
"Will they be able to do it, challenging all fronts? I think they need to strengthen in the market."
- Tim Sherwood was speaking to Tribalfootball on behalf of BetBrain