An MRI taken Thursday revealed the strain.
Porzingis originally hurt the shoulder during a block attempt at the rim during Monday's loss to New Orleans.
Interim coach Kurt Rambis says Porzingis is officially listed as day-to-day.
The team will take a cautious approach with its prized rookie.
"I would be the last person to recommend that he comes back and puts himself in a situation where he could cause more harm to himself," Rambis said. "That would be ridiculous of us as an organization and a medical staff. They won’t allow that to happen. He’s going to have to ... feel very comfortable that he can go out there and perform."
In other injury news, tests on Jose Calderon's right quadricep yesterday revealed a deep contusion, the Knicks say. He will be out for an extended time and is currently using crutches to get around.
Porzingis will miss his fifth game of the season on Friday, but his durability thus far has allayed concerns that his frail frame might not be able to handle an NBA season.
"He understands that it’s tough -- it’s a physical game and we’re encouraging him to get inside, which makes it more physical. But he’s such a fierce competitor that he’s going to take on challenges, it doesn’t matter what the situation is," Rambis said.
The Knicks' future hinges in large part on the development of the 20-year-old rookie. It is unclear at this point if Porzingis will play for the Latvian National team this summer or choose to remain with the Knicks.
Regardless of when he returns to the court, Porzingis' drive, work ethic and durability have injected a dose of optimism into a Knicks franchise that needs it.
"He has this incredible desire to be a complete all-around ball player and be one of the great players that have ever played this game," Rambis said. "He’s really driven, he really is. So it doesn’t surprise me that he was going to try to figure out how to make it through the season and just deal with everything."