John Terry suspected Kalidou Koulibaly was a prank caller and hung up on Chelsea's new centre-back when the Senegalese star asked to take his old shirt number.
Koulibaly had the 26 shirt at Napoli and was eager to retain it at Chelsea, but decided he should check that was OK with Terry.
No first-team player at Chelsea has worn 26 since Terry departed at the end of the 2016-17 season, so it was a courtesy call that Koulibaly considered important.
Terry eventually happily gave his blessing and urged the new recruit to bring in more trophies, yet Koulibaly revealed that initially the former Blues and England captain thought he had a rogue caller on the line.
The 31-year-old said: "I was nervous a bit because I was waiting to sign my contract in Chelsea. It happened the day before. I was happy, and the second thing is I wanted to know which number was free.
"Speaking with the team manager, he told me some numbers, and he didn't tell me the 26. I said that John left it in 2017 and nobody took it from this time. So I was asking myself if it was retired or maybe nobody wanted to take it."
Koulibaly turned to a former Napoli and Chelsea hero to get hold of Terry.
"I asked Gianfranco Zola, who I know very well, about the club, about the structure and the supporters, and I asked him for John's number because I wanted to ask for the jersey," Koulibaly said.
"I called him and at the beginning he didn't believe that it was me, he believed it was a joke. He put down the phone and called the team manager to ask if it was really me.
"I know that it's a very important number for him, and it's very important for me because I took it to Napoli and I wanted to keep it for here at Chelsea.
"When he told me 'yes', I was really happy because I know what he did for the club and the supporters and the city here, and I knew it was important to ask him. He gave me his answer and I was happy.
"I wanted to tell people I had asked him before, because I didn't want to be disrespectful to a legend of the club."
Chelsea begin their season on Saturday at Everton, who are bossed by another Stamford Bridge great in Frank Lampard, as the Premier League gets under way.
Koulibaly, speaking in a news conference on Wednesday, said former Blues coach Antonio Conte had tried to sign him for Chelsea in 2015, but this time "the stars were in a good line".
"This team is a fantastic team of winners, of big stuff. I want to give them everything on the pitch," Koulibaly said. "I'm 31 with a good club in a good city. I hope I will stay here a long time."
He said it was important not to expect him to directly match up to Antonio Rudiger, who moved on to Real Madrid at the end of last season.
Comparisons are bound to be made, given he will be taking Rudiger's spot in central defence, but Koulibaly said: "I'm Koulibaly. I'm not Rudiger. I don't have the same skills, I don't play like him. I have another style.
"I will try to do my best and try to give solidity to the team. I know it will be difficult because I come from Italy and Premier League football is difficult. But I'm very motivated and want to show everybody Chelsea made a good choice with me."