Luke Falk arrived at MetLife Stadium on Monday, having never thrown a regular-season NFL pass. He left preparing for a potential showdown with Tom Brady.

With franchise quarterback Sam Darnold already sidelined by mono, the Jets lost backup quarterback Trevor Siemian to what appeared to be a bad ankle injury midway through the second quarter of a 23-3 loss at MetLife Stadium, and were forced to turn to Falk, who completed 20 of 25 passes for 198 yards.

“It’s been a weird week. A week ago I was on the practice squad, and tonight I’m standing in front of [the media] after playing in a game,” Falk said. “It’s a weird series of unfortunate events for those two guys, and I just want to do my best and help my team win.”

Siemian left the stadium on crutches and with a walking boot on his left foot, leaving Falk — a practice-squad player prior to Darnold’s illness — likely to start Sunday’s game at the defending Super Bowl champion Patriots.

“If my number’s called, I’ll be ready to roll,” Falk said.

With the Jets trailing 13-0 midway through the second quarter, Siemian was crushed by former No. 1-overall pick Myles Garrett, who landed on the quarterback, bending his left foot backwards.

But disaster arrived long before the injury.

Siemian, who entered with 25 career starts, led the Jets to 7 total yards in the first quarter, and finished 3 of 6 for 6 yards, with no passes completed past the line of scrimmage.

In his place came a second-year, sixth-round pick, who looked more comfortable in the unfamiliar role.

“He went out there and gave his all. That’s all he could do,” wide receiver Robby Anderson said. “He gave [us] a chance to make plays. He stepped in, he didn’t let the moment get too big. He did all he could.”

Falk, who had previously been waived by the Titans and Dolphins after starring at Washington State, led the Jets to their only points during the drive in which Siemian was injured, completing one pass for 1 yard.

“I thought Luke did a really good job,” coach Adam Gase said. “He started off kind of slow. I was just trying to ease him into the game a little bit. … Luke is very confident. Once we got out of that first series, you could just tell he was calm. It was like we were at practice.”

Trailing 16-3 late in the third quarter, Falk connected with Anderson for a 36-yard gain, and brought the Jets to Cleveland’s 12-yard line, but the offense turned it over on downs. In the fourth quarter, Falk nearly led the Jets into the end zone, but Le’Veon Bell’s fumble at the 7-yard line ended another disappointing drive.

“Hopefully Trevor’s all right. You never want to see a guy that you spend so much time with go down like that,” Falk said. “I think there’s a lot of learning to do. I think there are some positives. I don’t think it’s as bad as what the score might show, but we definitely gotta be better. I felt good. A play here, a play there, it’s really a different ballgame. I felt calm, cool and collected and I just wish we made a few plays here and there.”