Johnny Manziel Accused of Wrecking L.A. Mansion

1:21 PM PT -- Johnny is denying EVERYTHING ... telling TMZ Sports the allegations are bogus.

"I never rented a house in the hills," Manziel says.

"I've been staying with a friend when I've been in L.A. which, as of late, has not been much. This guy is upset with a friend of mine and dragging me into it."

Johnny Manziel is accused of trashing one of the most famous homes in the Hollywood Hills -- with the owner telling TMZ Sports the ex-QB has turned it into "the worst frat house you've ever seen."

Here's the deal ... celebrity real estate magnate Danny Fitzgerald says he rented his legendary Weidlake mansion out to a guy named Bryan Chase back in July -- only to learn Johnny and his pal, OVO Ryan, moved in too.

FYI, the property has been used in TONS of TV shows including "American Idol" -- and has been rented by huge stars like The Weeknd and Ne-Yo (who Fitzgerald described as "great" tenants).

Fitzgerald says Johnny had been footing the bills -- paying the $25,000 per month rent and all of the utilities with checks with his name on it. But he's several days past due on the October rent so Fitzgerald sent him a pay or get out notice.

But that's just the tip of the iceberg -- Fitzgerald says the guys have been raising hell in the home and pissing off the neighbors.

In fact, Fitzgerald says the cops have been to the home several times to deal with raging parties.

Plus, Fitzgerald says the home has been trashed ... with more than $180k in damages to windows, doors and more.

"It's like this is a movie about a frat house ... but the worst frat house you have ever seen. It's like Charles Manson is living here."

Fitzgerald says he plans to sue.

We reached out to Manziel for comment -- so far, no word back.