So close and yet so far removed, four-time Olympic medalist Shawn Johnson found last week's U.S. trials in San Jose a "weird" experience after watching her former team mates from the sidelines.

One of the most recognisable faces in gymnastics with her sparkling smile and bubbly personality, Johnson abruptly retired from competition last month aged just 20 because of recurring knee problems stemming from a skiing accident in 2010.

She had fervently hoped to qualify for her second Olympic Games, which start later this month in London, but instead she will now be travelling to the British capital as an observer.

"It's been strange and weird watching the other girls at the U.S. Olympic trials just because I was training to be out there myself," Johnson told Reuters on the final day of competition at the HP Pavilion.

"It was bittersweet for me, the whole idea of coming and sitting in the stands. When I watched the girls training, I had a pit in my stomach.

"But I've kind of accepted it and gotten used to it. I came here to support them all the way and make sure they have somebody to cheer them on and not have to be critical."

Johnson, who won Olympic gold on the beam at the 2008 Beijing Games along with silver in the team, all-around and floor exercise competitions, had a special reason for being in San Jose during the trials.

Procter & Gamble, the household products maker, announced a grant of $75,000 on the eve of the trials to support youth sports development in U.S. gymnastics and Johnson will be their special correspondent at the London Games.

'HUGE HONOUR'

"It's a huge honour," said Johnson, who took up gymnastics in 1995 at the age of three and went on to claim three gold medals at the 2007 world championships in Rome - in the team, all-around and floor exercise competitions.

"It touches my heart because it affects all the kids and gives them the opportunity to be a part of fitness, and nutrition and that's kind of the route I want to take going forward. I want to have a voice in that area."

Asked what else she had planned for the future, now that competitive gymnastics was in her past, Johnson replied: "I want to go to college, obviously go to London and just kind of figure out the rest of my life.

"I'm not sure about it all yet. At college, I will study business probably but I'm sure that will change, just like any college student," she said with a smile. "And hopefully continue what I am doing now."

Johnson has high hopes for the U.S. women's team at the London Games where they will be bidding to emulate the so-called 'Magnificent Seven' who won the country's first team gold medal in women's gymnastics at the 1996 Olympics in Atlanta.

"This team is incredibly strong," she said of a line-up comprising world all-around champion Jordyn Wieber, trials winner Gabby Douglas, Alexandra Raisman, Kyla Ross and vault specialist McKayla Maroney.

"The dynamic and camaraderie that the girls have between each another is one that makes for a great mix among the five girls.

"Compared to 2008, it's going to be just as hard of a competition and Russia and China are going to be right up there. But I believe our girls will be ready to take them on. I think we will be the team to beat."