The offer represents the most advanced approach for the 18-year-old so far, with reports from Brazil indicating it surpasses the financial level Gremio had been seeking before opening serious negotiations.
That has immediately placed Hull at the front of the queue for the attacking midfielder's signature.
According to multiple reports in Brazil, Hull's proposal is official and is already being analysed by Gremio's hierarchy.
While no final decision has been made, the offer is reportedly being treated seriously behind the scenes, largely because the financial package goes beyond the figures Gremio have publicly been associated with in recent months.
Journalist Fabio Vargas revealed Hull are offering €17m up front, plus a further €3m in performance-related bonuses.
The proposal also includes up to €5m from a future sale, in addition to a percentage of any capital gain generated by a subsequent transfer.
Over recent months, Gremio have repeatedly been linked with valuations between €15m and €20m for the attacking midfielder.
Hull's package effectively reaches that threshold immediately and could eventually climb beyond €25m, making it the most concrete and financially significant move for Mec so far.
Gremio have been working on a contract extension for Mec until 2031, a move designed to strengthen their negotiating position and maximise the fee they can command from any sale.
Club officials have openly acknowledged they expect substantial European interest in the player and believe the teenager is capable of generating a major transfer fee in the coming years.
Mec's rise through Gremio's academy has been closely watched in Brazilian football, with his performances at youth level prompting comparisons with several of the club's previous breakout talents.
Hull's willingness to move so early and so decisively in the window reflects the scale of their ambition following promotion, with the club keen to strengthen across multiple positions before the new Premier League season begins.
Should the deal go through, Mec would arrive in England as one of the most significant investments of Hull's recent history, with the club hoping his technical qualities can translate quickly to a higher level of competition.
Gremio's hierarchy are expected to weigh the financial package carefully against their wider plans for the player, with a final decision likely to take shape over the coming weeks as talks continue, particularly given the scale of interest already shown from elsewhere in Europe.