The old saying is that a watched pot never boils.

Since the beginning of free agency last week, Pistons president Stan Van Gundy hasn’t been looking much at his phone. When something happens, it’ll happen.

That something is news on Pistons restricted free agent Kentavious Caldwell-Pope, who is himself anticipating an offer sheet with a big pay raise over the $3.7 million he made last season. Some estimates project Caldwell-Pope to get a max offer, with a four-year deal at around $100 million.

It’s been five days, but no phone call. Not yet.

While many of the top free agents are off the board, the Pistons have watched as some of the potential suitors for Caldwell-Pope have gone in other directions.

The Philadelphia 76ers gave J.J. Redick a one-year, $23-million deal. The Brooklyn Nets, long rumored to be the hottest destination for Caldwell-Pope, have a max offer sheet for Washington Wizards forward Otto Porter.

While the Nets await that outcome, Caldwell-Pope is on hold.

And while the Pistons were waiting, they also reached an agreement with free-agent combo guard Langston Galloway, for a reported three years and $21 million.

The Pistons already were over the salary cap and with the Galloway move, possibly made it more difficult to get Caldwell-Pope.

“The issue is that KCP’s maximum salary is $24.8 million, so if he got an offer sheet somewhere else for the maximum and Brooklyn — once Otto Porter gets the max — seems like the only reasonable option to do that,” NBA cap expert Nate Duncan told The Detroit News.

“If that happens, (the Pistons) — as it stands right now — could not match and could not go over that apron for any reason at any time during the season, once they sign Langston Galloway.”

The tax apron is the point at $6 million above the luxury-tax line ($119.3 million) where teams are more restricted in what they can do financially.

In essence, the Pistons would be hard-capped and wouldn’t be able to go over that apron ($125.3 million) to do any business. In order to do that, they’d have to shed some of their current salary — and not just a smaller dollar amount.

Duncan estimates that teams want to operate at somewhere between $4 million and $5 million below the hard cap.

With some current estimates, the Pistons are at about $105.2 million without Caldwell-Pope’s salary.

If he’s in the max range of about $24.8 million, that would be $130 million — or about $5 million over the hard cap. One solution: move about $9 million in salary.

Looking at the salaries, the Pistons have some options: Jon Leuer is due about $10.5 million and Reggie Jackson and Tobias Harris $16 million each. There could also be combinations of salaries to reach the desired number.

“What this augurs is that they’re going to need to get off of at least $7 million to $8 million in salary just to be able to run their team next year, if in fact, KCP gets the max,” Duncan said. “It may be if they moved on from Boban (Marjanovic) and his $7 million, they might feel like they had enough, it’d be about $4 million to work with and they could make some moves later in the year if they needed to.

“Or maybe they could string together a couple guys like Ish Smith, Stanley Johnson and Henry Ellenson as well. Those calculations assume they waive Michael Gbinije, who has $500,000 guaranteed as of July 15.”

Gutting the rosters of some of their younger first-round picks such as Johnson and Ellenson seems highly unlikely, but the Gbinije decision could be a tough one.

The next issue is assembling a full roster. Even with Gbinije, the Pistons would have only 13 players on the roster. Recent reports indicate the Pistons made a multiyear contract offer to reserve center Eric Moreland, meeting the NBA minimum of 14 roster players.

They also could consider two other players on two-way contracts to play with the Grand Rapids Drive and be eligible to play with the Pistons, if needed.

Another option for Caldwell-Pope would be to accept the qualifying offer of $5 million and play out this season, becoming an unrestricted free agent for next summer — where a bigger payday could await.

All the Pistons can do is watch.

And wait to see what happens.