By Gene Cherry

BEIJING (Reuters) - World champion Tyson Gay will be fully fit for the biggest challenge of his life when he runs in the highly anticipated 100 meters at the Beijing Olympics, his co-coach told Reuters on Thursday.

"By the time he steps on the line, he will be 100 per cent," twice Olympian Jon Drummond said in a telephone interview. "Otherwise, why show up?."

"There is nothing to detour his confidence," former sprinter Drummond said after working with Gay for three weeks in Germany.

Gay strained his hamstring in the preliminaries of the 200 meters at the U.S. Olympics trials in early July.

The 100 meters, his only individual event in Beijing, is expected to be the athletics highlight of the Games with Jamaican world record holder Usain Bolt, his compatriot Asafa Powell and Gay all gunning for the gold medal.

The 100 meters heats begin on August 15 with the final the following day.

Gay set an American record of 9.77 seconds in the quarter- finals of the U.S. Olympic trials. He then won the final in a wind-assisted 9.68 seconds, the fastest time ever under any conditions.

Drummond said even without the strain, Gay would have needed to rest after running the 9.68 seconds.

"I don't care what anybody says, that took a little out of the body," he said.

"When you have a Grade one strain, a lot of times the muscle has just been overworked," he added. "It's not a serious injury.

"We set some goals and he has met everyone of them."

(Editing by Ed Osmond)