Teams interested in making the trade would have to compensate the Lions with a valuable return and give Slay a new deal, Schefter adds.
Detroit has reportedly been trying to sign Slay to a long-term contract since the conclusion of the 2019 regular season.
Slay displayed his desire for an extension in 2019 by skipping the team's offseason work. He has one year remaining on the four-year, $48.1-million deal he signed in 2016.
The 29-year-old leads the Lions in both interceptions (19) and passes defended (99) since 2014.