Are we sure Sam Darnold is the only member of...

Sam Darnold wasn’t the only one feeling sick.

With the franchise quarterback sidelined with mono for Monday night’s game against the Browns, the Jets lost backup quarterback Trevor Siemian to a gruesome ankle injury midway through the second quarter of a 23-3 loss at MetLife Stadium, and were forced to finish the game with Luke Falk receiving his first regular-season action.

With the Jets trailing 13-0 midway through the second quarter, Siemian went back to pass on a third down and was crushed by former No. 1 overall pick Myles Garrett, who was penalized for roughing the passer and violently fell on the quarterback. Siemian’s left foot appeared to bend backward.

Siemian, 27, remained down on the ground for several minutes but managed to walk off the field. Shortly afterward, the former Broncos starter headed to the tunnel, with the assistance of trainers, and was then ruled out for the rest of the game. The severity of his injury was unknown.

But disaster arrived long before the injury.

Siemian, who entered with 25 career starts but hadn’t played in a regular-season game since 2017 — spending all of last year on the bench behind Kirk Cousins in Minnesota, before signing with the Jets — led the Jets to 7 total yards in the first quarter. When his day was done, he had completed 3 of 6 passes for 6 yards, with none thrown past the line of scrimmage.

“We’ve got so many talented players that I’m going to lean on,” Siemian said before the start. “Jamison [Crowder], Robby [Anderson], Ryan [Griffin] and everybody up front has a ton of experience. I’m fortunate in that sense. I can lean on these guys and it makes my job pretty simple.”

In Siemian’s place came Falk, a second-year, sixth-round pick, who’d only ever seen preseason action and was promoted from the practice squad earlier in the day. Unexpectedly thrown into a leading role, Falk promptly led the Jets to a field goal — he threw one pass for 1 yard — and looked more prepared than the former Denver starter.

Falk, who had previously been waived by the Titans and Dolphins after starring in Mike Leach’s Air Raid offense at Washington State, completed 16 of his first 20 passes for 170 yards, without completing a turnover. In the fourth quarter, Falk nearly led the Jets offense into the end zone, but Le’Veon Bell’s fumble at the 7-yard line ended the team’s best shot at a touchdown.