TOKYO (Reuters) - Japan's Seven & i Holdings must act fast to negotiate a takeover bid from Canada's Alimentation Couche-Tard that has "historic implications", according to a fund manager at shareholder Artisan Partners.

Couche-Tard, owner of Circle-K convenience stores, last week sounded out Seven & i about a possible acquisition, a deal that would be the biggest ever overseas buyout of a Japanese company. A potential deal value hasn't been disclosed and there's no guarantee a transaction will happen.

Artisan has been a critic of Seven & i's management and structure since 2019, and fund manager Ben Herrick said the board should negotiate with Couche-Tard while the offer remains friendly to increase the chances of a positive outcome for stakeholders.

Artisan said in a statement it is an active - not activist - shareholder, which engages with corporate management and boards.

Herrick declined comment on whether his fund has been in contact with Seven & i management. Seven & i representatives did not immediately respond to a request for comment on the views expressed by Herrick.

"The most important part of this deal, for both the reputation of the board and for corporate Japan, is that shareholders receive a fair, independently managed process," Herrick, associate portfolio manager of Artisan's International Value team, said in an e-mailed response to questions from Reuters.

"The outcome of this process has potentially historic implications," he added.

U.S.-based Artisan holds 0.85% of Seven & i's outstanding shares, according to LSEG data. Bloomberg News earlier reported on the fund's views on the bid.

Artisan, as well as activist investors Third Point and ValueAct Capital have criticized Seven & i, which operates the global 7-Eleven convenience store chain, for low returns and poor corporate governance.

Herrick said Artisan's efforts have help bring about an independent board and chairman at Seven & i that can hold the company's management accountable and "realize the value of this world-class asset".

"We did not arrive at this juncture because corporate oversight and capital allocation were best in class," he wrote. (This story has been corrected to remove the activist description for Artisan in paragraphs 1 and 9, and to add company statement in paragraph 4)