The former Chelsea and Arsenal forward was a free agent, having left Brazilian club Corinthians earlier this month.
Newsonline report that Willian, 34, has already been training with Fulham ahead of sealing the move.
Also, the West London club are bringing in Dan James in a loan move from Leeds,
SPORTTransfer deadline day: Willian returns to West London as Bamba Dieng lands in EnglandPublished on September 1, 2022By John Owen Nwachukwu
Fulham have completed the signing of Willian, The former Chelsea and Arsenal forward was a free agent, having left Brazilian club Corinthians earlier this month.
Willian, 34, has already been training with Fulham ahead of sealing the move.
Also, the West London club are bringing in Dan James in a loan move from Leeds,
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The Wales international was also a subject of interest from Tottenham this summer.
Fulham also had a bid for Ben Brereton Diaz rejected by Blackburn on the deadline day.
Meanwhile, Marseille forward Bamba Dieng is on his way to Leeds to undergo a medical after the two clubs agreed a fee.
Leeds are also interested in Wolves striker Hwang Hee-Chan.