Claudio Ranieri says he knows everything about Chelsea after revealing he was invited to watch Maurizio Sarri’s Chelsea side in training for a week before taking charge at Fulham just over a fortnight ago.

Ranieri returns to Stamford Bridge where he spent four years from 2000-2004 for the West London derby on Sunday but admitted his reconnaissance trip will provide little help in attempting to stifle their rivals.

Prompted about the trip, Ranieri said: “I know everything, but believe me it’s difficult to stop them.

“I asked, and Maurizio invited me. I was there one week and we had lunch after the training session.

“He was very kind. We spoke normally but when I don’t have a job I often go around and watch all the teams.

“I also went to watch [Jurgen] Klopp at Borussia Dortmund.

“I don’t want to stay at home. I look and I go around the world; it’s important to look at what’s happening.”

However, Sarri too has his own piece of espionage to rely on having been invited to watch Ranieri’s Fiorentina side in the late ‘90s, which the 67-year-old conceded he had actually forgotten.

“When we met [recently], he said ‘do you remember I came to visit you? I forget everything, even what happened yesterday!” Ranieri said.

“He said ‘Claudio, do you remember, when I came, you were having a meeting with young players and I asked if I could come to watch your training sessions?’ I said ‘yes of course’,” he continued, before jesting that Sarri’s trip will provide him with no clues anyway since he is so prone to tweaking his team selection and tactics. “I am the Tinkerman, I change everything!”

Ranieri’s tenure at Craven Cottage got off to a spectacular start last weekend when Fulham clinched a vital three points in a thrilling 3-2 win against fellow strugglers Southampton. Yet, the Fulham manager knows his team’s rickety defence, who are still yet to keep a clean sheet this season, will be put to the cosh by Eden Hazard and co.

“But I think Sarri is not inspired by me, he’s a very good coach, because he arrived so late at the highest level.

“He deserves it. He has a lot of jobs in his career, and he deserves where he is.

“Sarri plays very well with the right philosophy; Sarriball.”