Arsenal hero Paul Merson says Willian will prove a transfer coup.
Willian arrived in the summer as a free agent from Chelsea.
Merson said, "I can't believe Chelsea let Willian go. I know they've gone out and get special players, but there's nothing to say they're going to hit the ground running.
"In Willian, you've got someone there who is ready-made. I like who they've signed, but they cost a lot of money, and their wages are probably the same as Willian.
"Frank Lampard has now. He hasn't got four years. That's management, I'm not being horrible. Even if Frank wins the league this year, it doesn't mean he's going to be there in four years' time! We know that, and how it changes.
"Who is to say this isn't going to take time for Chelsea? And I don't think they've got time at the moment."