The debt market is showing concern about Seven & I Holdings Co.’s $21 billion (¥2.21 trillion) deal to buy Marathon Petroleum Corp.’s gas station business, even as equity investors grew more positive on the purchase.

The credit rating of the world’s largest convenience store operator was cut by Moody’s Investors Service from A1 to A2, the sixth-highest level, citing "an expected spike in leverage” after the company’s biggest planned acquisition. Other rating firms have also put the retailer’s credit scores under review for potential downgrade.

For share investors, the acquisition of Speedway gas stations may be an encouraging sign that the retailer is aggressively pursuing global growth at a time when the population is shrinking at home. The bond market, on the other hand, is raising questions about what the price tag would mean for the company’s relatively strong credit ratings.