Marcos Alonso has completed his move to Barcelona from Chelsea.
Meanwhile, Chelsea boss Thomas Tuchel reckons the capture of Cucurella will ease the pressure on Ben Chilwell.
The England left-back is looking to get back up to speed after missing most of last season with a long-term knee injury.
“It absolutely helps,” Tuchel said at a press conference on Friday.
“It helps Ben to escape the pressure of ‘I have to deliver’ and ‘We need you absolutely now’.
“Ben is very ambitious and he couldn’t wait to come back to team training. He looks better and better and at the same time it seems that he needs a little bit more time to adapt to the rhythm and physicality of matches, which is absolutely normal.
“It’s a very demanding league and we have to take care about him, not just throw him in.
“He is impatient and we will never expect him to be fully patient, but he knows – we speak a lot about it – that everything needs time.
“He will get the time and still we will try to put him on the pitch as soon as possible because he was and is a huge asset for us.”