Jayson Tatum met with the media on Sunday following the Boston Celtics’ Game 7 loss to the Philadelphia 76ers in their NBA first-round playoff series and explained why he wasn’t able to play.

in the early afternoon on Saturday, Tatum was initially listed as questionable with left knee stiffness, But that status changed approximately two hours before tip-off and Tatum was ruled out for the win-or-go-home showdown in Boston.

Tatum confirmed he was feeling tightness in the back of his left knee and was technically still in the “return to play protocol,” which requires a progression from light activity (such as an exercise bike or jogging) to non-contact activity, then practice with no restrictions on contact over a 48-hour period.

The training staff and Tatum stuck to that plan and that meant being unavailable on Saturday, despite the stakes of a Game 7.

If the Celtics had advanced to the second round, Tatum said his status would have been day-to-day and he would have been available to play at some point against the Knicks.

Tatum added that he felt an injury like this may have been inevitable after returning from his torn Achilles sustained last year. (His knee injury was to the left leg, while the Achilles rupture occurred in his right.)

“I guess a little to be expected,” Tatum said, via CelticsBlog’s Noa Dalzell. “I was away for 10 ½ months and then came back, and I was playing every other day. I was playing 36 to 40 minutes. So it’s not unusual that something would come up.”

“It was just kind of tough because rehab was just going so well the entire time,” he added. “I guess it was inevitable at some point that I was gonna have to deal with was something, and it just kind of came at the worst possible time.”

Tatum’s availability was in question after he left Thursday’s Game 6 in the third quarter with what was called “left knee stiffness” and did not return. Philadelphia went on to win that game, 106-93, to force a decisive Game 7 at TD Garden.

Following the game, Celtics coach Joe Mazzulla didn’t seem overly concerned, saying that Tatum “just got stretched, got some treatment” and appeared to believe that he would play in Game 7. However, neither he nor the medical staff had all of the necessary information to make a considered decision.

The Celtics lost by nine points, 109-100, and Tatum had averaged 23.3 points, 10.7 reobunds and 6.8 assists during the series’ previous six games. So it’s not unreasonable to speculate that had he been available to play, Boston would have advanced to the second round for a rematch with the New York Knicks.

“All things considered, for me to even be able to come back and play — and play at the level I was playing that, you know, even at 80, 85% — one of my legs is still smaller than the other one,” Tatum said, via WEEI’s Justin Turpin.

“And so now that I get a long offseason to really get back to 110%, i guess that’s the silver lining of it all.”

After returning in early March, Tatum appeared in 16 regular-season games for Boston. He averaged 21.8 points, 10 rebounds and 5.3 assists while shooting 33% on 3-pointers.