Tim Sherwood has questioned the wisdom of Tottenham Hotspur's signing of seven players without Premier League experience last summer, suggesting that the policy was not without risk.

The technical director, Franco Baldini, oversaw the investment of £110.5m in the group and the most expensive, Erik Lamela, who joined for a club record £30m from Roma, has now been ruled out for the remainder of the season with back trouble. Tim Sherwood said that another, Etienne Capoue, would most likely not play again this season because of an ankle problem.

Sherwood talked up the form of Christian Eriksen and the recent impact of Nacer Chadli in central midfield but the overall picture has been one of inconsistency. Vlad Chiriches, Roberto Soldado and Paulinho have fired mostly in fits and starts.

Sherwood described himself as a "firm believer that Premier League experience is key" and he highlighted Everton's recent business as the blueprint for success.

The Merseyside club, who will go fourth with a draw or better at Sunderland on Saturday, added Gareth Barry, Romelu Lukaku and James McCarthy on 2 September from Manchester City, Chelsea and Wigan Athletic respectively – the first two on loan deals. They had taken Gerard Deulofeu on loan from Barcelona earlier in the summer.

"You can buy someone who has never played in the Premier League and he comes over and he is a revelation but it's more of a risk doing that," Sherwood said. "If you want to look at any team, you've got to look at Everton and what they've done in the transfer market. It's second to none.

"On deadline day, they look like an average side but, all of a sudden, they make three signings and it turns them into what they are now. You've got Gareth Barry with 534 games or whatever it is in the Premier League – crucial for any club – while Lukaku was the best young player last season on loan at West Brom and you have the acquisition of McCarthy.

"And then there's Deulofeu who, as everyone in the development phase of football knows, can be anything he possibly wants to be. He is showing that now."

Lamela's first season in English football has been a disaster, with the Argentina winger having started only three league games. He has not played since 29 December because of, initially, a thigh injury and now a back problem that Sherwood said would sideline him for their remaining five fixtures. It also threatens his participation at the World Cup finals.

"He had some treatment from the Roma physios and our guys – I think he's been pretty much everywhere," Sherwood said. "It's a similar injury to the back problem that Chiriches had and we're pleased to have Chiriches fit so our guys have done a good job with him. Lamela's probably not going to play [again] this season. He's been out a very long time. He's going to need a pre-season before he can play.

"He's basically been out of the picture because of his injury and hopefully he's using this time to learn English. That will stand him in good stead for when he's eventually fit."

Sherwood was asked how Lamela's English was coming on.

"Qué?" he replied.

Capoue was injured at Norwich City on 23 February and Sherwood said it was "very doubtful whether he will play between now and the end of the season" while none of the club's other casualties – Kyle Walker, Jan Vertonghen, Mousa Dembélé and Soldado – were "close" to a return.

Walker feels like a World Cup worry for England, having carried a groin problem since mid-February. His last appearance came in Tottenham's Europa League home tie against Benfica on 13 March and, although Sherwood maintained there was plenty of time before the finals, Walker's situation did not sound entirely positive.

"The physios don't know [a time-frame], to be honest," Sherwood said. "I think they are just taking every day as it comes. It is improving. It's certainly not going the other way but he's got to train. It's been a long time.

"We're concerned [more] immediately because he's not fit and, probably, it's very doubtful that he'd be fit for next weekend as well. But he's still got a lot of time before the World Cup and there'll be a few friendlies for England as well. Kyle is one of the best right-backs and I'm sure he'll be on that plane to Brazil even if he doesn't make an appearance for Tottenham by the end of the season."

Sherwood believes that Tottenham "should be good enough" to beat each of their remaining opponents. After Saturday's trip to West Bromwich Albion, they face Fulham (home), Stoke City, West Ham United (both away) and Aston Villa (home).

"If we do win every game, it is fantastic for the club and who knows where that might take us?" Sherwood said. "People are not talking about us now but hopefully we can come on the rails. I have been to enough horse races when someone comes late."