World champion Tyson Gay has pulled out of a meeting with world record holder Asafa Powell over 100m in Friday's Golden League meeting in Brussels.
Gay also pulled out of last weekend's meeting in Zurich
"The American is feeling too tired after the world championships to face Asafa Powell on Friday," race organisers said in a statement.
Gay won gold in the 100m, 200m and 4x100m relay in Osaka.
Britain's Christine Ohuruogu has also pulled out of the 400m at the meeting due to fatigue.
The world champion is feeling the effects of a very heavy programme after returning from her one-year suspension for missing three out-of-competition drug tests.
She could only finish fifth behind Sanya Richards in last Friday's Golden League meeting in Zurich in a slow time of 51.32 seconds.
"Christine is very tired and quite simply has run far too many races in such a short time frame," said Ricky Simms, organiser of her racing programme.
"She has not given up on her season. A few extra days' rest and she believes she can do herself justice on Sunday at the Berlin Golden League meeting.
"It is essential after pushing herself so hard in Osaka that she does pace herself after what has been a hectic programme in the last few weeks.
"She is still hungry for another couple of races before the season ends."
Powell comes into Friday's meeting after setting a new world record of 9.74 seconds at the Rieti Grand Prix in Italy on Sunday.
Race organisers said that they had also tried and failed to tempt Gay into a 200m race against the other Osaka medalists and compatriot Xavier Carter, who missed the World Championships.
Carter looked impressive at last week's Golden League meeting in Zurich, winning the 200m in 19.92 seconds.