The former Chelsea defender has found himself frozen out in the last six games under Milan coach Paulo Fonseca.
Alerted to the situation, La Gazzetta dello Sport says Napoli have made an approach to Milan for Tomori, while Juventus have also expressed interest.
However, if they're to sell, Milan management would prefer not to sell Tomori to a direct rival.
Instead, they'd favour selling Tomori abroad, which raises the prospect of a return to the Premier League. Brighton, West Ham, Wolves and Aston Villa are all interested.
Milan will seek €20-25m to sell Tomori next month.