Duke Energy Corp. will need another way to shuttle natural gas to customers in the U.S. Southeast if the troubled Atlantic Coast shale pipeline fails to overcome legal setbacks, Chief Executive Officer Lynn Good said.

“Atlantic Coast pipeline was sized and designed with a time frame to meet the needs of our customers,” Good said Monday in an interview with Bloomberg Television at the BNEF Summit in New York.

That time frame is in limbo after a federal appeals court vacated key permits that allowed the pipeline to cross the Appalachian Trail, a decision lead developer Dominion Energy Inc. is...