The Brazilian helped his country to Copa America glory on home soil this summer, and will join up with the Blues squad on their tour of Japan next week.
Willian is in the final year of his contract at Stamford Bridge and has been linked with a £30 million move to Barcelona.
According to the Express, Lampard wants to watch the 30-year-old in training before deciding if he will be awarded a new deal.
The Blues have previously used a policy of not awarding players over 30 extensions of more than one year.
However, a FIFA-imposed two-window transfer ban could change the Premier League club’s plans as Lampard looks to keep his squad together.
Willian’s compatriot David Luiz signed a two-year renewal in May despite being 32.
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