Darren Anderton believes that players who leave Tottenham will see their performances drop without Mauricio Pochettino to help develop their careers.
Pochettino has guided the club to Champions League group-stage qualification in the last two seasons, with Spurs' close-knit squad finishing second in the 2016-17 Premier League table.
Despite Spurs' push for success, Kyle Walker has left for Manchester City in a £50million deal while Danny Rose went public earlier in August regarding his frustrations over the club's wage structure and ambition.
Walker was sent off on his Etihad Stadium debut for Man City against Everton, and former Spurs midfielder Anderton has warned the likes of Rose that there are few coaches like Pochettino,
"Pochettino has made every player at Tottenham better and everyone says how good the players are, but it's because Pochettino has improved them," Anderton told sportingbet.com. "He makes everyone work hard but it clearly pays off throughout the season.
"I'm a massive fan of his high intensity training, which really shows its worth during Christmas. You only have to look at last year when Spurs were comfortably beating everyone over that period.
"Players that leave Tottenham won't perform to the same level they were at when they were at Tottenham. When they haven’t got a manager like Pochettino pushing them as hard as they can go and being on their back the whole time, their performance levels will drop.
"It's vital that Tottenham keep Pochettino, because if players start to leave, then he could get disillusioned himself and want to leave, so they have to keep this team together.
"Levy will have to have 100% faith in Pochettino and will give him what he wants, with everything he's done and the way the club is moving forward he can't afford to break that up. So I'm sure that wherever possible Levy will back Pochettino's transfer targets."
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Spurs are set to announce the £42m signing of Ajax defender Davinson Sanchez and have also brought in Southampton goalkeeper Paulo Gazzaniga as a back-up to Hugo Lloris and Michel Vorm.
The club are also set to capture £23m Serge Aurier from Paris Saint-Germain, but Anderton believes Spurs still need new faces to survive in the Champions League.
"Above transfers, the most important thing for Tottenham was to keep everyone and it's a shame to see Kyle Walker go, but Trippier is ready to step in and take his position," he added.
"Tottenham do have to keep strengthening, even if it's not their first eleven, with the Champions League they need a strong squad, it's not just about the 11 players, but Spurs need to bring in a couple more quality players and freshen things up a bit.
"I don’t know too much about Sanchez and it's a different test for him in the Premier League. Tottenham defend properly and don’t take chances so Pochettino would have wanted someone who fits into that role.
"Pochettino will want Alderweireld to play along side Sanchez to learn as much as possible, he's the perfect manager to work with young players."