Caeleb Dressel dropped farther and farther behind, a far cry from the dominant swimmer he was at the last Olympics.

In his first major competition since a long layoff, Dressel finished 29th in the preliminaries of the 100-meter freestyle at the U.S. nationals on Tuesday, not even close to qualifying for the world championships in an event he won in Tokyo two years ago.

Dressel touched the wall behind all seven other swimmers in the last of eight morning heats.

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His time of 49.42 seconds was a whopping 1.79 behind top qualifier Ryan Held, who swam one heat earlier, and a sobering reminder of how far Dressel has to go after walking away from swimming last summer during the world championships in Budapest, Hungary.

He didn't come close to making the U.S. team in the 100 free for next month's worlds in Fukuoka, Japan. Dressel's time at the IUPUI Natatorium was nearly 2.5 seconds off his gold medal-winning performance (47.02) at the Tokyo Games two summers ago.

Dressel was one of the biggest stars at those Olympics, winning five gold medals.

But the 26-year-old Floridian mysteriously left the sport for an extended break and only returned to competition only last month at a minor meet in Atlanta.

Clearly, Dressel has a long road to recapture the form that made him the successor to Michael Phelps as the world's most dominant male swimmer.

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Dressel still has three more chances to qualify for the world championships, having also entered the 50 free as well as the 50 and 100 butterfly. But, based on his lack of speed in his first event, it likely will be an uphill climb to claim a spot on the powerful U.S. team.

Then again, Dressel is surely more focused on getting back to top form in time for next summer's Paris Olympics, though he hasn't publicly revealed his plans or goals.

In keeping with his reluctance to speak with the media, he declined interview requests after his dismal start to the national championships.

Dressel returned to the pool in the evening to cheer on his Florida teammates and take a spot in the "C" final after several other competitors decided not to take a second swim.

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Dressel actually went slower than he did in the morning, posting a time of 49.64.

Still, his return to swimming has been welcomed by both teammates and rivals, all of them cheering for him to recapture his previous form.

"We're all just really happy that he's here and competing," said Katie Ledecky, who also swims for the group coached by Anthony Nesty. "There's so much that you all don't see on a day-to-day basis, just the joy that be brings to the pool deck every day and impact he has on his teammates."

Nesty acknowledged last week in an interview with The Associated Press that he was uncertain how the swimmer would perform in such a high-pressure meet after a long layoff.

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"I think he came back re-energized," Nesty said. "He stayed busy. Was he on a weekly training cycle? No. But I think he still did some swimming on his own, some lifting on his own. At that point, you kind of let them do their own thing."

When Dressel decided to return to swimming, Nesty eased him back into his training.

"We started him with a really light load," the coach said. "He didn't get a full load until Week 10."

Nesty said it was important for Dressel to get away from the sport. The swimmer previously discussed the pressure and mental health struggles he faced ahead of the Tokyo Olympics, which included panic attacks and depression.

"I think he needed it," Nesty said. "At that point, all you can do is support your athlete. He has a good group of people that care about him and support him. Obviously, I'm happy he's back in the sport. That's where he belongs."

Dressel provided the lone public update on his layoff in an Instagram post last September.

"I haven’t swam since worlds and can honestly say I have been happy without swimming. I really miss it though," he wrote. "I know I can have swimming and happiness. I had them both at one point in my life and I’m working on it. If you need a break, take one. I’ll be back."

After his first swim in Indy, it's clear he's not there yet.