It was not an April Fool's joke, unfortunately.

The UFC really did lose its lightweight title matchup between Tony Ferguson and Khabib Nurmagomedov on April 1, which was scheduled to headline Saturday's UFC 223 in Brooklyn. Ferguson withdrew due to injury.

Luckily, featherweight champion Max Holloway agreed to take Ferguson's place, even though he hasn't been training regularly.

One of the greatest challenges he'll face over this week is making weight. Holloway, 26, needs to be 155 pounds by Friday's weigh-in.

To get a better idea on where Holloway is now -- and what the next five days will look like -- ESPN spoke to renowned nutritionist George Lockhart, who is overseeing Holloway's weight cut in New York.

ESPN: What was the initial conversation between you and Holloway's camp in regards to accepting the fight?

Lockhart: I got the call from Max's manager asking, "Hey man, can we do this?" I was like, "What's his weight?" And he's heavy, obviously. He hasn't been training. I had to call Max and get the basics of everything, how much he's been eating and what he's been eating. It's almost beneficial he's been eating poorly, because once these guys clean up their diet, you see that weight drop really quick.

Brian [Butler-Au, Holloway's manager] told me, "We're not doing this unless it's done healthy. He's not doing permanent damage to his body doing this." I promised him, "There's no f---ing way we're getting to a point where we risk his health or the longevity of his career."

ESPN: Are you able to say what he weighs right now?

Lockhart: This is going to be tied for the biggest weight cut I've ever done. The other one that was this much [not Max], we only had four days to make it. The circumstances were very different, but as far as time goes, we actually have more time on this one.

ESPN: Under these circumstances, what is the most Holloway could have weighed where you would have agreed to attempt this cut?

Lockhart: I think, like, 187 pounds would have been an automatic, "No way in hell."

Featherweight champion Max Holloway accepted a five-round fight against Khabib Nurmagomedov on six-days notice. Josh Hedges/Zuffa LLC/Getty Images

ESPN: So, Holloway has a substantial amount of weight to lose by Friday. What's the strategy?

Lockhart: They're not gonna lose that amount of weight in six days. You can't lose that much weight -- but you can cut that much weight. Losing weight is losing calories and your body leaning out. In this case we need to do both: lose weight and cut the water.

This is rare -- I want people to know that -- but he's going to be an extreme 'keto state.' We need him to burn as much fat as humanly possible. Whereas every other fighter we're working with this week at UFC 223 has already lost the fat, coming in shredded and just needing to cut water, Max has to be in a state where he's burning fat.

He's going to be running a few hours this week. And some people who run marathons or condition a lot might say that's not a lot, but when you're depleting your body and asking it to do more, that's the challenge. Typically, we fuel fighters up to give their body what they need. If I say, 'Hey, we need you to go on a run,' we'll fuel the body up for it, so the body wants to do it. What I told Max is, 'I'm going to be asking you to do things your body is not going to want to do.' And that's when it becomes a mental thing.

Then we have to make sure we're recovering. Ice baths, massages, stretching -- it takes time for muscles to recover. If we're running, running, running, and he's sore the day of the fight, it's going to have a negative impact.

ESPN: What did you sense is Holloway's mindset, approaching this type of weight cut?

Lockhart: Max knows what he has to do, and he's excited. ... I'm not gonna lie, I think he almost likes the amount of weight he has to lose, because it's a challenge. Max has always said he doesn't want to fight guys people think he can beat. He wants to fight the guys people think he'll lose to. When you give him a challenge, he excels. And that's the main reason I agreed to do this with him.

ESPN: What will he be eating during the next five days?

Lockhart: We'll cook his food in coconut oil, sesame oil. We'll get him seared ahi. He's from Hawaii, he'll like that. No carbs. We'll give him some spinach or something like that, but no carbs that will fuel him. We want his meat portions to be the same. Let's say I go from six ounces of chicken breast to four ounces. I may lose 40 to 60 calories, but if I increase the meat content and he's able to run an extra 20 minutes, not only did I burn those calories, but also the water attached to it.

ESPN: Ideally, what will Holloway weigh when he goes to bed on Thursday evening, the night before the weigh-in?

Lockhart: I'm hoping within four pounds of 155. We'll be doing a hot salt bath in the morning. We control the most variables with the bath.

ESPN: You said right off the bat that you won't allow this to endanger his health. How will you monitor that?

Lockhart: Say we put him in a bath, 106 degrees, and it takes him 15 minutes to crack a sweat. Then let's say we put him in for an extra 15 minutes and crank the temperature up to 107, 108 -- if he loses like a pound, and we have eight pounds to go, there's no way we're doing it.

We have a skin test, where you pull the skin and if comes down slowly and you still have a lot of weight to lose, you call it off. You test the colors of the fingernails. The eyes, obviously. We monitor his heart rate and blood pressure. We'll make sure those are good to go. My team's process is different than others. At the end of the day, I'm not gonna be like, 'You know what, I think he's good.' If he's not good, we're gonna get him the f--- out of there as soon as possible. I'm not going to let anyone get injured.