Knicks swingman Tim Hardaway Jr. indicated his absence will last past the Christmas season.

In his first remarks since going down with “a stress injury” in his lower left leg, Hardaway called it a “serious injury,” said he’s not going to “force the issue” and declined to give himself “a deadline’’ to return despite feeling progress.

Hardaway has been out for 12 days and will be re-evaluated early next week when a more definitive timetable may be issued.

“This is serious,” Hardaway Jr. said. “I’m going to take everything slow. This is a serious injury.”

When asked directly if he felt he will be back by the start of the new year, Hardaway demurred.

“The goal is just to get better first,” Hardaway said before the Knicks faced the Nets at the Barclays Center on Thursday. “That’s the goal. I’m not giving myself no deadline. I don’t want to get to that point and be upset and down on myself. I don’t want to give myself a set date on when I should return. I’ll do what I can to get this right. When I’m confident and ready to go, then we’ll see.’’

Medical experts told The Post that Hardaway has either a stress reaction or stress fracture — both of which take several weeks to heal. A stress fracture in the leg could result in a season-ending complete fracture if played on. A less serious stress reaction, inflammation of the bone, can result in a stress fracture if not rested.

Hardaway declined to say whether it was a stress fracture.

“I’m not going to rush it,” Hardaway said. “I’m going to wait until I’m 100 percent mentally ready to go. If it was the playoffs, I’d be out there right now. But you got to be smart and do what’s best for you. I trust the team. They’re playing hard, playing smart.”

Hardaway, the Knicks’ second-leading scorer at 17.8 points per game, had played with various ailments — calf, ankle and foot soreness — before this injury. He said his latest wasn’t due to compensation, in his view.

“It felt like a bruise one day,” Hardaway said. “It started to hurt a little more and I got evaluated. It came out to be what it is now. I don’t believe in [overcompensation]. It’s just separate.”

Hardaway still is using a walking boot but said he feels OK when he doesn’t use it.

“I’m out there walking around without it on,” Hardaway said. “It feels a lot better. The pain isn’t as severe as it seems.”

Hardaway said he’ll have “a better idea of what’s going on” after his evaluation — which likely will include a bone scan. He’s allowed now to dribble in place and take standing shots — without putting pressure on the left leg.

“It’s all new to me,” Hardaway said. “I definitely want to be out there. You have to do what’s smart for your career. It’s a stress injury. You can’t really rush anything.”

The game Thursday marked the seventh without Hardaway. The Knicks caught a break as a soft stretch of the schedule coincided with the injury. Six of their past seven opponents, including the Nets, had records under .500.

“It’s tough — like someone took something away from me,’’ Hardaway said. “I know the guys at the beginning were, ‘What’s going on? What happened?’ It came out of nowhere. It sucked.”

This is Hardaway’s second stint with the Knicks, and it was going along so well. His trade to Atlanta, where he spent two seasons, enhanced him in various ways.

Nets coach Kenny Atkinson, a former Hawks assistant, oversaw that growth.

“I saw the work he put in,” he said. “[Coach Mike Budenholzer] did a great job holding him accountable, sending him to the D-League. But Timmy, he really came a long way. It was such a transformation I thought. When he came to Atlanta — what’s the word? — he wasn’t in elite shape. I didn’t think he came in with a defensive mentality. It’s great to see him playing great in a Knicks uniform. That’s a great story, really, his transformation.”