Fields averaged 8.8 points and 4.2 rebounds a game last year with the New York Knicks. The Raptors can't make the offer sheet official until July 11, at which point the Knicks would have three days to match.
The deal was first reported by ESPN. The Raptors declined to comment on the report when reached by The Canadian Press, but Octagon agency, which represents Fields, confirmed to The Associated Press that the deal is three years and about US$20 million.
Fields was named to the NBA all-rookie team in 2011, when he was fifth among rookies in rebounds with 6.4 per game and sixth in scoring with 9.7 points per game.
Fields was also reported in several media outlets to be part of a sign-and-trade deal between the Knicks and the Phoenix Suns for Canadian point guard Steve Nash, who is said to be highly coveted by the Raptors. Signing Fields to an offer sheet would severely impact the Knicks' reported plans.
— With files from The Associated Press.