Any final exit by the U.K. from the European Union that worsens business conditions through increased tariffs would threaten the sustainability of Nissan Motor Co.'s U.K. operations, the Japanese carmaker's chief operating officer (COO) has cautioned.

Nissan, which employs 7,000 people at the U.K.'s biggest auto plant in Sunderland, northeastern England, urged in June for an "orderly, balanced Brexit".

Its latest warning, however, comes as the EU cautions the U.K. that it has fewer than 10 days left to secure a deal to govern trade from next year.