The NFL said: "Our Personal Conduct Policy applies equally to everyone in the NFL. We will handle this allegation in the same way we would handle any issue under the Policy."
"We are seeking a full understanding of the facts, while ensuring that we do not interfere with an ongoing law enforcement investigation. We will take appropriate action as warranted based on the facts."
The NFL's personal conduct policy requires owners, players and other employees to "refrain from 'conduct detrimental to the integrity of and public confidence in' the NFL."
The NFL in the past 20 years has at least twice sanctioned team owners for personal conduct violations.
In 2014. the league suspended Indianapolis Colts owner Jim Irsay for six games, and also fined him $500,000, after he pleaded guilty to a charge of driving while intoxicated.
In 1999, the league suspended then-San Francisco 49ers owner Eddie DeBartolo Jr. for the entire season that year, and fined him $1 million in connection with a gambling scandal in Louisiana.
Kraft's Patriots won their record-tying sixth Super Bowl earlier this month.