Fitch Ratings said Monday the ratings of Nissan Motor Co. could be negatively influenced if the proposal to include General Motors Corp. in its alliance with Renault SA becomes a reality even if positive synergies from the association are taken into account.

Apart from channeling financial investments into GM, both Nissan and Renault might have to give the U.S. auto giant additional financial support, Fitch said.

"As many of the problems GM currently has are deeply rooted and cannot be resolved in a short period of time, it is expected that a considerable amount of Renault and Nissan's management resources will be spent revitalizing GM's operations for a long time, if they are involved in GM's management," it said.

Nissan currently has weaker sales than expected as a result of its low level of new model introductions, Fitch said. In addition, the automaker has a lot to do to achieve its medium-term goals, including successful and continuous new model introductions. The possible three-way alliance might hinder Nissan's efforts to achieve its management goals, the international rating agency said.

The major area of benefits from an alliance would be cost reductions through the widening of joint procurement projects, sharing of research and development achievements, having common platforms for vehicles and more efficient use of production facilities, according to Fitch.