MIAMI — The Mets are off to the best 10-game start in franchise history, but they have not exorcised all their demons.

The catching position remains the shakiest of positions for the Mets; it has been that way for years, and with word Wednesday that Travis d’Arnaud has suffered a partial tear of the ulnar collateral ligament in his throwing arm, you can plant a big red flag behind home plate.

Jonathan Lucroy did not sign until March 12 with the A’s, a veteran catcher many expected the Mets to sign. It never happened. They did not pony up. Now, here we are with the d’Arnaud injury.

The job belongs to Kevin Plawecki, and the Mets have made it clear they don’t want much offense from Plawecki, just handle the pitching staff. Baby steps.

The irony is that Zack Wheeler started Wednesday night against the Marlins at Marlins Park as the Mets were looking for their eighth straight win, finally making the dream-team rotation a reality, but now there is no d’Arnaud, who came over with Noah Syndergaard in Sandy Alderson’s brilliant trade of R.A. Dickey to the Blue Jays.

Alderson had a terrific offseason, landing the likes of Todd Frazier, Jay Bruce and Adrian Gonzalez, but the hole at catcher was never plugged, unless you count the signing of Jose Lobaton.

The Mets decided to hand the job to the injury-haunted d’Arnaud and Plawecki, hoping for the best, and 10 games into the season d’Arnaud’s Mets future is in doubt because he most certainly is headed for Tommy John surgery.

Now it’s Plawecki’s job. He needs to fall in line with the next-man-up mentality the Mets have fostered under Mickey Callaway. It’s now or never for the 35th pick of the 2012 draft.

Plawecki has a lot of support from the front office, coaching staff and teammates, so don’t expect any bold moves just yet.

In this game, the baseball always seems to find the weakest link defensively. The same can be said for injuries. The weakest position is usually the most susceptible to injury.

The Mets are at a catching crossroads.

Plawecki is a worker. Moments after Tuesday night’s stirring 8-6 comeback win over the Marlins, Plawecki was in the batting cage with hitting coach Pat Roessler working on driving the ball to the opposite field.

Plawecki was hitting .158 with one RBI before Wednesday night’s game. Over his previous 16 at-bats entering the game, he had just one hit — a single — good for an .063 average. He needs to improve quickly.

The dreadful A’s are already 4-8 and five games back in the AL West, so maybe Lucroy will be made available at some point. But for now it is Plawecki and Wednesday’s backup, Tomas Nido.

Don’t expect the Mets or Alderson to be in panic mode. That is not the general manager’s style.

“We’re thankful we have Kevin,” said assistant GM John Ricco, who is traveling with the team. “There was a lot over the years, ‘Oh, you can move one because you have the other,’ but that is a position where you can never have enough depth. I really believe Kevin has taken a big step forward.”

Plawecki has his chance and said he believes he is better equipped now to handle the catching load.

“It’s just having more experience and having relationships that I’ve built with this staff,” Plawecki said. “There is no doubt in my mind I feel very comfortable playing. I’ll play every day if I could.’’

It’s his job now.

Plawecki needs to reward the faith Mets management has shown in him. It’s really that simple.

“Right now, we have to consider Plawecki is the guy,” Callaway said. “Don’t worry about the offense, especially if you are playing every day.”

Last season Plawecki caught 29 games for the Mets. Over three seasons, he caught 144 combined games. Now the Mets are counting on him to lead the way behind the plate.

That’s a lot to ask.

The Mets were shaky behind the plate before this latest d’Arnaud injury. Plawecki needs to handle the job or the Mets will be caught short once again.