With Kristaps Porzingis missing his third straight Knicks game with a sore Achilles tendon, a leading medical expert in foot/ankle injuries told The Post the 7-foot-3 Latvian is suffering from tendinitis, should play less minutes and go on a special program to strengthen the tendon.

The good news, the expert from Northwestern Memorial Hospital said, is Porzingis likely is too young at 21 to be suffering from Achilles tendinosis, which could result in a career-ending rupture. However, the expert said Porzingis is more prone to Achilles tendinitis than virtually all other NBA players.

“For sure people who are of advanced height put more strain on the tendons, their height and length mechanically puts more stress,’’ Dr. Anish R. Kadakia, associate professor of orthopedic surgery and fellowship director of Orthopedic Foot and Ankle Fellowship at Northwestern University, told The Post. “The Achilles is the most relevant because it has to support your whole body weight.’’

Porzingis said he had never had Achilles pain before developing soreness Christmas Day, but played through it for two games before being shut down last week in Houston. Coach Jeff Hornacek said before the Knicks’ 105-104 loss to the Bucks that the tendon was still “stiff’’ but hoped to get Porzingis into a practice Thursday and try to play him Friday.

Kadakia, who has not had Porzingis as a patient, said his recommendation is for Hornacek to ease up on the playing time for now. (The Knicks medical staff is not permitted to speak to the media.)

“That’s the problem,’’ Kadakia said, “leading the team in minutes played. That’s really a lot for him at this point, the excess strain and the length of time he’s playing. A couple of things can be done — decrease playing time and at the same time have a regimented physical therapy for the Achilles to make it stronger for the future, a regimented program to build up tolerance. He’s not ready for it coming from a college or European schedule.”

Kadakia added Porzingis can’t have his A-level game if he plays with Achilles tendinitis, but no medical proof exists he’s more prone to a rupture.

“It can affect jumping and running because he can’t generate the same force because of the pain and inflammation surrounding the tendon,’’ he said.

If Porzingis had disease of the tendon causing the pain — tendinosis — it would be big trouble. That could only be shown on an MRI exam or ultrasound, and Porzingis hasn’t had either.

“A young person, it’s usually a strain from overuse,’’ Kadakia said. “He just needs rest and focused physical therapy.’’

An NBA source said the Knicks aren’t planning to pursue Suns defensive forward P.J. Tucker despite his ties with Hornacek.

Tucker shut down Carmelo Anthony in last month’s meeting between the teams, and Hornacek regarded Tucker as one of his favorite players in Phoenix. Tucker said upon Hornacek’s return to Phoenix last month, “It was really tough watching an amazing coach” get fired.

“I wasn’t happy about that with the way it happened because I felt like it was more our team than him,’’ Tucker said.

A report stated the Knicks consider Tucker a trade target.