"To my fantasy owners ... who lost without my help I’m sorry," M.G. wrote on social media.

Gordon was a monster this year -- averaging 25.15 fantasy points per game -- but a knee injury sidelined him while many needed him the most in fantasy playoffs Thursday night.

Of course, the NFL superstar was probably the reason you were IN the fantasy playoffs in the first place ... but he's still apologizing nonetheless.

"Crunch time in these playoffs and I couldn’t come thru !!"

But hey, it coulda been worse ... at least fantasy owners had a heads-up a couple hours before kickoff to swap him out of the lineup.

As for his teammate, Keenan Allen ... the same can't be said -- and THAT'S the apology we're all still waiting for!!!