Chicago Police Supt. Eddie Johnson had “a couple of drinks with dinner” before driving home and slumping over in his vehicle, Mayor Lori Lightfoot disclosed Friday.

One day after the police superintendent she inherited requested an internal affairs investigation of himself, Lightfoot refused to say whether Johnson should have been driving or whether he should have been given a sobriety test.

Lightfoot told the Chicago Sun-Times she would await the outcome of the internal investigation before determining whether the rules were bent to protect the boss and whether to hold Johnson responsible.

Johnson was discovered around 12:30 a.m. Thursday near the 3400 block of South Aberdeen.

Police and Chicago Fire Department personnel who responded to a 911 call of a man slumped over in his vehicle allowed the superintendent to drive himself to his Bridgeport home.

“Everybody — whether it’s the superintendent or a beat patrol officer — has to abide by the rules ... It was the right thing to call for an investigation ... We’ll see how that plays itself out,” the mayor said.

“I know what the superintendent told me, which is that he was … changing medication … He’d been out to dinner with some folks. He told me he was driving home. He felt ill and pulled over to the side of the road, which he believed was the prudent thing to do … IAD will sort out the rest.”

Lightfoot was asked whether she buys the superintendent’s story.

“I have no reason to doubt [it]. We know he’s had some medical issues. He’s on the other side of a kidney [transplant] operation, which is obviously very, very serious. There have been some issues with high blood pressure and so forth,” she said.

“When I take medication, sometimes it has side effects. I know from my parents. So, I take him at his word. The investigation will sort out the details. … We’ll see what happens.”

Did the mayor ask the superintendent if he had been drinking?

“I didn’t ask him that question specifically. He revealed to me that he had a couple of drinks with dinner,” Lightfoot said.

If Johnson had been drinking, should he have been driving?

“I can’t say that. I don’t think you can say that. But no matter what, we’ve got to let the investigation play itself out. He’s a grown man. He had a couple of drinks with dinner,” the mayor said.

Johnson has blamed Thursday’s incident on his decision to throw out the old prescription without replacing it with the new one.

The superintendent said he dismissed his driver after dinner, allowing him to go home to tend to his young family.

“Should I have had a driver with me last night? Yes, I should have,” Johnson said.

Johnson wants desperately to keep his $260,044-a-year-job — at least until April when he will be fully vested in his superintendent’s pension.

Lightfoot was reluctant to make a change heading into summer, when gang violence traditionally surges. But she has promised to evaluate the superintendent’s overall performance on a host of issues — once the summer was over.

That conversation has not yet taken place.

“We will have that when the time is right. Obviously, there’s a lot going on,” the mayor said.

Lightfoot was asked whether the incident would play a role in her decision on whether to keep Johnson on.

“I don’t want to speculate like that. I want to give him respect. We will see what the circumstances are. … We’ll see where the facts take us,” she said.

Three years ago, an end-run around the Police Board’s nationwide search for a replacement for fired Police Supt. Garry McCarthy allowed then-Mayor Rahm Emanuel to pluck Johnson out of obscurity, even though Johnson didn’t seek the job. Johnson at the time was the department’s chief of patrol.

Emanuel pulled it off by rejecting all three finalists chosen by the Police Board after a first nationwide search and by persuading the City Council to cancel the charade of a second nationwide search required by law.

At the time, the Police Board president was Lightfoot.

Now, the shoe is on the other foot.

Lightfoot is the mayor charged with choosing the superintendent. But she also has her hands full with a teachers strike. Firing Johnson — or pushing him to retire — would be another headache she doesn’t need at the moment.

“There’s not a lot of people ... who can be the leader of the second-largest police department in the country. Maybe there’s 10 or less who can actually do the job. ... I don’t take that decision lightly,” she said.

“He came in ... and really stabilized things when a lot of people felt like the department was unmoored. We have to give him credit for stepping into the breach when the department was under siege. I will take that, of course, into consideration.”