The New York Mets are having a frustrating season — both on and off the field.

While the team’s second-straight losing season is well documented, unreported till now is the challenge Comcast and Charter Communications are experiencing selling their combined 12 percent stake in the franchise.

The two minority owners have been trying since mid-summer to sell their stake — but the response has not been overwhelming, The Post has learned.

The sellers, working through investment bank Inner Circle Sports, hope to sign a deal before MLB’s Winter Meetings, which begin Dec. 9, two sources close to the matter said.

Comcast and Charter are hoping the end of the season will focus new interest in their stake — worth about $250 million, based on Forbes’ estimate that the team is worth $2.1 billlion.

It could be a tough sell.

The Mets 2018 attendance is down 9.1 percent from last season — which was off 11.8 percent from 2016, when the gate swelled because the team was the defending National League champ.

The Mets, which close out the season Sunday, will likely finish with the 15th-best attendance in the 30-team MLB, with roughly 2.1 million paid.

In 2016, the Mets drew 2.8 million fans.

There is another factor in the sale as well, sources said.

The sale is turning into a litmus test on the management capabilities of Mets Chief Operating Officer Jeff Wilpon, sources tell The Post.

“This is clearly a Jeff Wilpon play,” a source said.

Principal owner Fred Wilpon, 81, is expected to turn the team over to his son, Jeff, at some point in the not-too-distant future, sources said.

Not everyone is enthralled with Jeff’s management ability, sources said.

The selling minority owners are willing to consider a discount on the Mets $2.1 billion Forbes valuation, a source said — and should be happy if they get a valuation of over $1.7 billion.

Charter and Comcast bought the stake in 2012 to save the Wilpons from losing the Mets when the team was almost bankrupt. The cable companies have stakes in Mets sports network SportsNet New York, and did not want to see a change in ownership. They are not selling their SNY stakes.

Charter Communications declined comment, and Comcast did not return calls.