It's somehow getting worse for Jon Gruden, because his emails don't just include racist language ... now there's a report he also used homophobic slurs aimed at Roger Goodell.

Gruden, who already apologized for a racially insensitive email he fired off in 2011, reportedly referred to the NFL Commissioner as a "f*****" and "clueless anti-football p****" ... according to emails obtained by The New York Times.

Gruden also reportedly wrote Goodell should not have pressured former NFL coach, Jeff Fisher, to draft "queers" in 2014 ... referencing Michael Sam, the first openly gay player drafted into the NFL.

The alleged homophobic language might not sit well in Gruden's locker room ... he's currently the coach of the Las Vegas Raiders, who have defensive lineman Carl Nassib on the roster, the first active player who is openly gay.

According to The New York Times, Gruden fired off the emails from 2010 to 2018, when he was out of pro football and working as an analyst for "Monday Night Football" on ESPN.

Gruden reportedly aimed homophobic slurs at Goodell in several instances, as well as using other offensive language to describe NFL owners, coaches and media.

Even Barack Obama and Joe Biden were reportedly mentioned in Gruden's emails ... with Gruden ripping Obama during his 2012 re-election campaign and referring to Biden as a "nervous clueless p****."

As we reported ... Gruden's been on the hot seat since a 2011 email was uncovered, where he says NFL Players Association president, DeMaurice Smith, had "lips the size of Michelin tires."

Gruden apologized for the racist email a second time Sunday, after his team lost to the Chicago Bears, saying he doesn't "have an ounce of racism in me."

The new report also says Gruden mocked Caitlyn Jenner in his emails, after she received an award from ESPN in 2015 following her transition.

Gruden's currently in the 4th year of a 10-year, $100 million contract to coach the Raiders ... and it's unclear if he faces any discipline.