"Saturday Night Live" star Darrell Hammond isn't laughing about Thursday's presidential debate ... and is instead issuing a very stern warning regarding the country's future.

Darrell famously used to impersonate Donald Trump, Al Gore and Bill Clinton on 'SNL' ... but he told us he saw nothing funny about Thursday night's presidential face-off, calling the whole event sad and potentially dangerous.

This might sound odd coming from Darrell, who lampooned Trump for years, but he says fans should avoid mocking Trump's mannerisms ... because it makes him seem less dangerous.

These days, he thinks voters should take very seriously Trump's prior comments about wanting to become a dictator.

As for Biden? The 'SNL' announcer has empathy for 46, and says jokes about the president's frailty are cruel and unfunny ... as Biden clearly appeared not well through much of the debate ... something political pundits on both sides of the aisles have highlighted.

That being said, there's no doubt 'SNL' will tackle the presidential election when it returns this fall ... and DH thinks creator Lorne Michaels will find a way to appropriately add humor to the situation.

Though, Darrell has no plans to play 45 again -- cast member James Austin Johnson handles that these days -- he does say it was all fun and games in 2016, when everyone thought Trump's candidacy was a joke.

Darrell's no longer laughing, and thinks trying to create jokes from this situation is dangerous.

Darrell says there's no update yet on who will impersonate Trump or Biden on the upcoming 50th season of 'SNL.'

Jason Sudeikis, Taran Killam, and Alec Baldwin have all played Trump ... along with Darrel and James.