Gary Sheffield will be among those at Citi Field on April 14 when Dwight Gooden has his No. 16 jersey retired by the Mets.

Few people, if any, have been as close to Gooden on his journey from Tampa to Queens, with all the highs and lows — both on and off the field.

Sheffield is Gooden’s nephew — though they are just four years apart — and the two learned the game in Tampa together from Gooden’s father, Dan.

Sheffield’s mother, Betty, is Gooden’s sister.

“This is what my granddad [Gooden’s father, Dan] always envisioned: Both of us doing great things and what he did for the Mets, bringing them a championship,” Sheffield told The Post by phone this week. “To be rewarded with a jersey retirement is special not only to him, but to the whole family.”

And it’s an honor not even Sheffield was sure would happen, given Gooden’s issues with drugs and alcohol that have landed him in trouble numerous times over the years.

“That’s always the case when you have someone with a substance abuse problem,’’ Sheffield said. “You always think about those things. You always think about the worst-case scenario and thank God that hasn’t happened.”

From their days together in Florida, when Sheffield learned how to hit against a young Gooden, they both went on to have lengthy major league playing careers.

And when Gooden would find himself in trouble, Sheffield was often there to help — including paying for rehab.

Over the years, Sheffield, now 55, has spoken about the toll Gooden’s problems took on him, and he did again this week.

“That’s something people don’t understand with my career,” Sheffield said this week. “I used to have to endure those things while I was playing. I was able to be successful when the club was relying on me, and having to do things for [Gooden], it was harder than people think. Every time he relapsed or did anything else, we, as a family, we all were hurting. I was able to block it out when I got on the baseball field. That was kind of my outlet.”

Sheffield ended up hitting 509 homers — including the 500th of his career at Citi Field while with the Mets, 15 years ago this month — and is looking forward to being back in Queens, where he ended his career in 2009.

And he still credits Gooden with much of his success as a player.

“I learned everything from him: the hardship of baseball and the fun part of baseball,’’ Sheffield said of Gooden, 59. “I owe everything to him. My mom is his big sister, and it was like we were brothers from birth. My mom, she always encouraged me to be tougher and better than him, so it became competitive when we were young.”

That relationship withstood a lot.

“We always did everything together — unless he was doing the wrong thing, and then he didn’t want me around,’’ Sheffield said with a laugh. “He taught me a lot. Even when he was going through his stuff, he always told me ‘Don’t follow what I’m doing.’ So I listened. And it was important he did that, because he acknowledged what he was doing wasn’t a good thing. When somebody has substance abuse problems and can acknowledge that, that’s awareness.”

As Sheffield got older, he said, he gained a better understanding of Gooden’s issues.

“My family and my parents were always positive people about his situation and said, ‘It’s not him, it’s a disease,’ ” Sheffield said. “So I understood it a little better. But it was always scary.”

Like many around baseball, Sheffield wonders what Gooden could have done if substance abuse hadn’t gotten in the way, but he hasn’t given up hope that both of them could still end up in Cooperstown.

“The rules and the Hall of Fame have changed,” Sheffield said. “They’ve changed the goalposts, lowered the goalposts. Him being right [under] 200 wins and doing what he’s done, I think if you’re gonna let a lot of these guys in, he deserves consideration because he dominated his era. When someone does that, you reward him. Yeah, he had issues, but so did everybody else. Hopefully he gets that honor as well. I don’t know what’s gonna happen with that, with either of us.”

But he’s confident in Gooden’s place in the game and with the fans.

“I think people appreciate him,’’ Sheffield said. “They stuck by his side, through his ups and downs. He had a lot of highs and a lot of lows and kept battling. We had a close family that always supported him, no matter what he did — or what he didn’t do. So just to come out here at the end is all that matters.”