Just how well Ethiopian Olympic champion Kenenisa Bekele and Oregon-trained British world gold medallist Mo Farah have progressed in their preparations will be gauged over 5,000 metres at this weekend's Prefontaine Classic Diamond League meeting.
"Kenenisa is getting better by the week, so the race should be very competitive," Bekele's manager Jos Hermens told Reuters.
"He needs races to get in shape, so if it will be a good fast race, it will be a good effort for him."
The Ethiopian world record holder stormed to Olympic titles in both the 5,000 and 10,000 metres at the 2008 Beijing Games before a 2010 calf injury kept him off the track for more than a year.
The Somalian-born Farah, meanwhile, has become the world's top ranked 5,000 metres runner and number two in the longer race.
His double medal haul at the 2011 world championships included a silver in the 10,000, making him a major British hope for the London Games.
Both he and Bekele will pursue distance doubles at London, adding to the budding rivalry.
Bekele has spent thousands of dollars to build a softer-surfaced track near Addis Ababa Ethiopia to train on.
"He is the only athlete in the world that I know of who has paid to put down his own synthetic track," Hermens said.
"The track was meant to be ready two months ago, but it became ready only two weeks ago. So he has just started his real training."
Farah, 29, trains with former New York and Boston marathon winner Alberto Salazar when in Oregon. He also has spent time in Kenya in preparation for the Olympics.
"I've had another year of running and I am feeling stronger now, compared to previous seasons," Farah said.
"I just need to stay injury-free and focused."
Other key races include 2004 Olympic champion Liu Xiang of China facing U.S. record holder David Oliver in the 110 metres hurdles and double Olympic bronze medallist Walter Dix racing 2004 Olympic champion Justin Gatlin in the 100 and Wallace Spearmon in the 200.
Another intriguing encounter takes place between Olympic gold medallist LaShawn Merritt and world champion Kirani James in the 400.
Women's races feature world 100 metres champion Carmelita Jeter facing former world gold medallist Allyson Felix in the 200 and world 400 metres champion Amantle Montsho racing former world winner Sanya Richards-Ross.