When Vice President Mike Pence abruptly canceled a trip this month to New Hampshire to discuss the opioid epidemic, White House officials steadfastly refused to say why.

The answer emerged on Monday, when it was revealed that a former New York Giants player who was expected to greet Mr. Pence at the airport in New Hampshire had pleaded guilty last week to trafficking fentanyl across state lines.

The man, Jeff Hatch, had worked at the Granite Recovery Center, which Mr. Pence was to visit on July 2. But the vice president’s aides canceled the trip after learning that Mr. Hatch was under federal investigation for drug trafficking, people briefed on the events said.

People familiar with what took place said that Mr. Hatch’s inclusion in the event was not a vetting failure — the investigation was not something that an advance check of the attendees would have uncovered. Instead, the people said, the vice president’s staff learned of the looming problem through law enforcement channels.