CLEVELAND — In the strongest sign yet of which way they are leaning before the trade deadline, the Mets have engaged the Red Sox on Zack Wheeler, The Post has learned.

The talks were described as in the early stages and that Boston is not the only club with whom the Mets are discussing Wheeler. In fact one source said as many as 10 teams have inquired on Wheeler and that the scout section at Citi Field was crowded Sunday when Wheeler started.

One comfort the Mets would have in dealing with the Red Sox is knowledge of their farm system. Until this year both Mets VP/assistant GM for scouting and player development Allard Baird and VP of player personnel Jared Banner held instrumental baseball operations roles with Boston.

Going into the final five games of the first half against the Yankees and Phillies, a Mets official had described those and the three after the break against the Marlins as a last determination if the club should sell. The Mets went 2-3 in those games so far, experiencing even more bullpen malfunction. The official described the Mets as realistic to their plight even as they were hoping to avoid being sellers.

The Mets are 40-50 at the break, the NL’s second-worst record. Baseball Reference gave them a half a 1% chance to make the playoffs. FanGraphs was a more optimistic, yet dismal 5.9%.

The Mets have indicated if they are going to sell that their priorities would be Wheeler, Jason Vargas and Todd Frazier, all of whom can be free agents after the season (Vargas has an $8 million option for 2020 with a $2 million buyout). Wheeler would be the piece that could land the Mets the most, namely because of the durability the righty has shown the last two seasons, the excellence exhibited over the final four months last year and the general perception of high-end stuff.

Wheeler was available last July, the Braves were the most aggressive pursuer, but the Mets decided no offers were enticing enough.