David Rudisha faces tough test at Kenyan Olympic trials

The 27-year-old world record holder faded to finish fifth in the Diamond League meeting in Shanghai in May and Rudisha came fourth in Stockholm two weeks ago.

"It won't be easy for him (at the trials). He could be facing a great challenge. As much as people respect him for who he is and his command of running, it won't be easy," Colm O'Connell told Reuters.

Irishman O'Connell, a retired high school teacher who has mentored many world-class athletes, was speaking in Eldoret in the Rift Valley, 350 kilometres north west of the east African nation's capital Nairobi.

"I have not followed him closely for a long time and I don't know whether he has been following our (coaching) programme. He has done very very little training with me this year," O'Connell said.

Rudisha has struggled for form and fitness since breaking the world record to claim the Olympic gold medal in London four years ago but he did win the world title in Beijing last year.

"Although I know he is a very experienced athlete, I am not sure if he is mentally fit. It would be misleading to say I knew his mental or physical strength. He has not been in touch for a long time," O'Connell said.