Willian joined the Blues from Anzhi Makhachkala in August 2013 and has gone on to win two Premier League titles and make 232 appearances.
However, the Brazilian playmaker has suggested that he needed time to adapt to life in England before being able to feel comfortable playing a different style of football at Stamford Bridge.
The 29-year-old told Sportsbeat: "I've learned a lot in my time in England. I have been here for five years, so I've learned many things.
"English football is not simple and it is very different to others. I think it's one of the strongest leagues in the world. There's no doubt that to play there you can't just arrive and play with ease. You must also understand how English football works, understand the Premier League.
"I already liked the Premier League before playing for Chelsea, and there's no doubt that it has been a huge learning curve to me over these five years."
Willian has been linked with a transfer away from the West Londoners, but the player still has over two years remaining on his contract.