Recent reports have suggested Chelsea are interested in the Brazilian in light of centre-back Ricardo Carvalho's transfer to Real Madrid.
The 23-year-old is highly-rated at Benfica, and Manchester City were linked with a bid earlier this summer.
In the wake of the Chelsea rumours, Vieira said: "We would only begin talks over an offer of about €40million.
"It would be impossible to consider any offer less than that because it would be bad business for us.
"I want David Luiz to stay at the club for this season."