The Lions know just the guy to appear on “Hard Knocks”: Raiders Coach Jon Gruden. (Justin Sullivan/Getty Images)

There are three ways for an NFL team to avoid being the subject of HBO’s “Hard Knocks” training camp documentary series: If they have a first-year head coach, if they have made the playoffs the past two seasons or if they’ve been on the show in the past 10 seasons. This year, that leaves us with five teams that can be forced by the league to appear: The Lions, Raiders, 49ers, Redskins and Giants.

The first team on that list thinks the second would be an ideal subject.

“I think Jon Gruden is an excellent choice for that show,” Detroit Coach Matt Patricia said Monday, per ESPN. “I think the Oakland Raiders and everything they’ve got going on right now would be fantastic viewing for everybody to watch.”

Patricia learned at the knee of Patriots Coach Bill Belichick, who probably would hold practices in a heavily fortified underground bunker if league rules allowed it. So his opposition to the show — where HBO’s cameras follow a team as it progresses through training camp — is hardly a surprise. In fact, Lions GM Bob Quinn claims that teams that play each season’s “Hard Knocks” squad, the Patriots included, try to use the show to figure out schemes and personnel. Detroit, which went 6-10 in Patricia’s rookie campaign, has all of three playoff appearances over the past 19 seasons and needs all the help it can get, would prefer to keep things under wraps.

“So, it’s real. Is it going to be a matter of a win and loss, I’m not sure,” Quinn said. “But we take the stuff that we do behind our doors pretty privately and pretty securely, so that’s something that is definitely a factor.”

If it had its druthers, the NFL would rather not force a team to appear on “Hard Knocks” and is always looking for volunteers, such as the Los Angeles Rams in 2016. One team that apparently won’t be raising its hand is the New York Jets, who cannot be compelled to appear because they have a new coach in Adam Gase and appeared on the show in 2010. According to Manish Mehta of the New York Daily News, the Gang Green brain trust would rather not have its training camp broadcast for the world to see.

The other teams on the “Hard Knocks” shortlist all have their merits. The Giants could be preparing a rookie quarterback to take over for Eli Manning. (They’re going to draft a quarterback, right? Right?) The 49ers will have quarterback Jimmy Garoppolo back from the season-ending ACL tear he suffered in Week 3 (though GM John Lynch publicly has stated his resistance to the idea). The Redskins will be looking to bounce back from an injury-ravaged 2018 season, with Coach Jay Gruden likely coaching for his job.

As for the Raiders, they don’t yet know where they’ll be playing their home games in 2019, but that situation seems likely to be resolved by July and the team’s final season in Oakland could give the show an interesting subplot. Plus, Gruden spent nine seasons in front of the camera with ESPN, so his on-screen comfort level is likely unmatched among his peers.

Just ask Quinn.

“Nobody wants to do it,” he said. “Except Oakland.”

Read more from The Post:

Women’s groups criticize the Browns after they sign Kareem Hunt

10 bold predictions for the 2019 NFL season

‘Football has been my love and passion’: Kyler Murray chooses the NFL over baseball

Justin Verlander says ‘rebuilding’ teams should offer Harper and Machado 10-year deals

NBA investigating Lakers-Ben Simmons contact for possible rules violations