Priceline Group Inc. will scale back expansion plans for its OpenTable dining service, prompting a $941 million write-down that overshadowed strong bookings in the online travel company’s core business.

Priceline Group paid about $2.6 billion for OpenTable in 2014. The purchase marked a departure for the company, which in the past concentrated its investment on travel brands. Executives at the time said putting dining options in front of travelers—the demographic group most likely to eat out—would provide a springboard for...