The proposed cap was disclosed Monday by a person familiar with the matter but not authorized to discuss it publicly.
Under the proposal, if multiple teams bid the capped amount, the player would get to choose the team with which he would negotiate. In theory, that could represent a step toward helping teams with less revenue bid on fairer footing with large-market teams such as the Dodgers and Angels.
There would be no cap on the contract between the Japanese player and an MLB team.
MLB and Japanese baseball officials have exchanged various proposals on how to improve the so-called posting system, which is the manner by which Japanese teams can make their players available to MLB teams before those players hit free agency.
It is unclear when -- or if -- this proposal might be adopted.
According to media reports in Japan, the owner of Tanaka's club -- the Rakuten Golden Eagles -- has said he would like to know soon whether Tanaka can be posted. Tanaka could negotiate a new contract with Rakuten in the meantime, perhaps with an escape clause for an MLB opportunity.
Tanaka, who would be considered the best pitcher in MLB free agency if he becomes available, went 24-0 with a 1.27 earned-run average for the Eagles.