The 31-year-old's existing deal at Stamford Bridge is due to expire later this month, and a final decision on his future is expected to be made following Saturday's FA Cup final.
A recent report claimed that Barca had offered the Brazil international a three-year contract to make the move to La Liga ahead of the 2020-21 campaign.
Here, Sports Mole looks at the shirt numbers available for Willian at Camp Nou should he join Quique Setien's side in time for next season.
Willian sported the number 22 shirt at Chelsea between the start of the 2013-14 campaign and the end of last season before taking on '10' following Eden Hazard's departure to Real Madrid.
Aside from a short spell with '88' at Anzhi Makhachkala, Willian has only ever worn '22' or '10' during his professional club career, but he has also had the number 19 and the number seven for Brazil.
The number 10 would not be an option at Barca, though, due to the presence of a certain Lionel Messi.
Arturo Vidal currently wears '22' for the Catalan giants, but there has been speculation surrounding the Chile international's future in recent weeks, meaning that his jersey could soon become available.
Philippe Coutinho took on '7' following his arrival from Liverpool, but the Brazil international is currently on loan at Bayern Munich and could be on his way out of the club permanently this summer, potentially opening up the famous shirt for Willian.
In terms of the top 20, the number 12 and number 14 - previously held by Rafinha and Malcom respectively - are also available, while '16', currently occupied by Moussa Wague, is also likely to be an option this summer.
A number of Barca players are thought to be on the transfer list this summer, though, and Ousmane Dembele's departure would see '11' become available, while Arthur is heading for Juventus at the end of the 2019-20 campaign, meaning that the number eight is also set to become vacant.