Cesar Azpilicueta fears for Chelsea’s title hopes if they are unable to sign top-class players during the remainder of the transfer window.
Chelsea head coach Antonio Conte has already spent more than £100m on bringing Alvaro Morata, Antonio Rudiger and Tiemoue Bakayoko to west London this summer.
But Conte has seen a number of departures from his first-team squad that won the Premier League last season, including Nemanja Matic, Nathan Ake and John Terry.
At last week's Premier League launch, Conte told Sky Sports News Chelsea's board know where he wants to strengthen the team and Azpilicueta says the Blues need experienced players to have any chance of retaining the title.
"Well, when you see the players we lost, and the players we have signed in, they are not the same," the Chelsea defender said.
"Obviously we have very good young players, but we have to know the reality that being champions is even harder the next season, we have experience of that.
"So we need players, also for the development of the young players, they need help from senior players, from top players, not to rush them in a position where maybe they are not ready to go at the moment but they will be in the future.
"So it is something that the club is working on with the manager, and hopefully we can get new signings in the next few weeks."
There seems to be no way back at Chelsea for the club's top scorer last season, Diego Costa, who remains in Brazil and has not reported back to Cobham since the Blues won the title last May.
His relationship with Conte remains strained but Costa told the Daily Mail he has been in touch with team-mates Cesc Fabregas, David Luiz and Willian, as well as former Chelsea boss Jose Mourinho.
He said: "I am always talking with the boys - particularly Cesc Fabregas, David Luiz and Willian. We have banter over WhatsApp. They ask how I am. They really love me for the person I am. If they didn't, they wouldn't be saying they miss me and love me.
"Jose [Mourinho] has called me, direct to my phone, just to check I am OK and to see how I am. He wished me good luck. I never had any problems with Jose, we have a strong relationship. Everyone was very sad when things didn't work out in the end for him at Chelsea."