The veteran midfielder left Fulham this summer and remains a free agent.
Willian told BBC Sport: “I decided to leave Fulham much before the end of the season in January or February. I had it in my mind that I would leave after speaking with my agent and family. It wasn't a decision made at the end of the season but a couple of months ago.
“I am looking at some options at the moment. I am thinking about possibilities in Europe, England, Saudi Arabia, Qatar and the MLS - just not Brazil as an option for me.
"I am trying to see all the possibilities and think about making the right decision right now. I have some offers already and this is the key moment to decide my next challenge.”
He also said, “I am working in the gym to be in good shape but, of course, it is different from training every day and being ready inside a club. But I am doing all I can to be in good shape for my next club.
"I think my level physically and mentally is great. I think I can play for three or four years more - maybe until I am 40 years old! I feel motivated and at a high level."
On Fulham manager Marco Silva, he added: "I only have good words to say about Fulham. It was an amazing two years and they treated me so well. I will always be thankful to them for opening the door to play in the Premier League again.
"The owners, people who work in the club, the guys and Marco Silva - he is a great coach and person."