TOKYO (Reuters) - S&P Global Ratings revised Nissan Motor's credit outlook to negative from stable and affirmed its BB+ rating, as it expected it would take the Japanese automaker longer to improve its business performance.

"The negative outlook reflects our view that the company's creditworthiness will continue to deteriorate if profitability does not improve and positive free cash flow is not secured," S&P said in a statement.

Nissan has increased sales incentives in a bid to correct high inventory levels, which have risen due to a slowdown in car sales in North America, the company's main market, S&P said.

(Reporting by Daniel Leussink; Editing by Jacqueline Wong)