Thomas Tuchel was delighted to complete the signing of Raheem Sterling from Manchester City but says Chelsea must continue to bring in "top quality" to compete for the Premier League.
The Blues sealed a £47.5m deal on Wednesday to add Sterling to their squad and, speaking with Sky Sports News, Tuchel described himself as "super happy", explaining that the England forward would be a "big improvement" to the Chelsea squad.
The London club are also closing in on the capture of Kalidou Koulibaly, with the Napoli centre-back in the capital for his medical after the clubs agreed on a fee around £32m.
However, the Chelsea head coach made it clear Chelsea - who have seen big-name players Antonio Rudiger, Andreas Christensen and Romelu Lukaku depart this summer - will have to keep on bringing in high calibre signings if they are to compete with City and Liverpool for the top honours this coming season.
"The stakes are high and we're competing not only against the best teams who have ever played in the Premier League but also the best coaches," said Tuchel.
"If you [then] see the transfer period and quality of coach at Tottenham, if you see the same at Arsenal, at Man Utd, we know what the challenge is. It's the toughest challenge you can [have].
"We come from sanctions, we come from losing top-quality players, key players, we are a club in transition, in transition of ownership, we were behind in the transfer race and we were behind in the table. So we have things to improve.
"The signing of Raheem shows what we're capable of doing, it shows the ambition of the club and the ownership and it's good because we're all here to win and compete.
"We love to compete and we love the challenge at the very top. For that we need signings of new quality players or otherwise there's no chance."
Tuchel describes the relationship between himself and co-owners Todd Boehly and Behdad Eghbali as "very close and intense" right now, with the pair assisting the head coach with transfers in the absence of a permanent sporting director.
The German says the trio are focusing on bringing in the best players possible to combine with the current squad and emerging young talents at the club.
"It started with analysing the last season, our performances, our squad, where we think we need to improve and can improve," said Tuchel, explaining the recruitment process.
"It's no secret we lost top players and we need to replace them. Even if they'd have stayed, we needed improvement to close the gap so we need now even more.
"We have top players and even more importantly we have a top team. But if we bring players in we need top quality with top character and then you're talking about the very, very best who play this game.
"What we'll never forget is the mixture because what makes Chelsea special is the amount of academy players and we'll never hesitate to give responsibility to them and push them because the mixture of it makes it special and exciting for me to be coach and part of it and this is the way to follow."
Tuchel refused to comment on links with Manchester United's Cristiano Ronaldo and Bayern Munich's Robert Lewandowski and said signing another forward is "not the priority" now Sterling has been added to the squad. Instead, his focus is on Chelsea's backline.
"I would not rule it out [signing another striker] but right now it is not the priority. The priority right now is defence, it's not a secret. From there we need to see what's possible," said Tuchel.
"We're competing against the two top teams but Tottenham did a very active and aggressive and early transfer period, they have maybe the strongest squad they ever had with one of the best coaches in the world, Man Utd are never shy of recruiting with a new coach and Arsenal had some big signings already so we need to keep the level up to be competitive."
Who will be on the move this summer before the transfer window closes at 11pm on September 1?
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