* Nissan may become single biggest shareholder in MMC

* Talks in final states, boards to meet separately Thursday

* MMC supplied cars which overstated fuel economy to Nissan (Recasts with talks, background on deal)

By Maki Shiraki

TOKYO, May 12 (Reuters) - Nissan Motor Co and Mitsubishi Motors Corp on Thursday confirmed they are discussing a possible capital tie-up, after sources said Nissan is in advanced talks to take a roughly one-third stake in its scandal-hit rival.

"Nissan and Mitsubishi are discussing various matters including capital cooperation, but nothing has been decided," the Japanese automakers said in separate statements, adding the boards would meet separately on Thursday to discuss the matter.

Two people familiar with the talks told Reuters earlier on Thursday the carmakers were in advanced negotiations over a deal that would see Nissan invest about $1.8 billion to buy a third of Mitsubishi, which is embroiled in a fuel-economy scandal.

If the 200 billion yen deal goes through, Nissan, Japan's second-largest automaker by sales, would become the largest single shareholder of much smaller Mitsubishi Motors.

The deal would give Nissan a bigger stake in Mitsubishi than its 15 percent holding in alliance partner Renault. The French automaker holds a 43.4 percent stake in Nissan.

Confirmation that discussions are under way comes just after Mitsubishi Motors on Wednesday said it had enough cash to weather the fuel-economy scandal, and warned that non-compliant data may have been used to calculate the fuel economy for more of its cars than previously announced.

Mitsubishi Motors admitted last month that it had supplied Nissan with mini-vehicles with overstated mileage levels.

Mitsubishi Motors shares had not traded so far on Thursday due to a glut of buy orders.

The automaker's market value has fallen around 42 percent or $3.0 billion since the scandal broke on April 20, on fears of hefty compensation costs, while sales of its mini-vehicles halved in April.

The automaker is part of the Mitsubishi business empire, or "zaibatsu", which was split up into independent companies after the Second World War.

It has strong ties with its sister companies, including Mitsubishi Heavy Industries Ltd, Mitsubishi Corp , and the Bank of Tokyo-Mitsubishi UFJ, which together with subsidiaries hold roughly a 34 percent stake in the automaker.

MILEAGE SCANDAL

Mitsubishi has admitted to overstating the fuel economy of four of its mini-vehicle models for the Japanese market - the Dayz and Dayz Roox which are marketed under Nissan's badge, and two other models under the Mitsubishi brand.