Nebiolo slates Americans who will miss Moscow.
Olympic 400metre champion Michael Johnson, along with world 100m title-holder Maurice Greene, have said they will not compete in the Russian capital because of the developing currency crisis and fears for their security.
But Nebiolo, the president of the International Amateur Athletic Federation, said in Berlin last night that if their President, Bill Clinton, could travel there, so should they.
"We have always been convinced that Americans are strong and they are not afraid of anything," Nebiolo said.
"But after we organised a meeting in Sarajevo they were afraid and now we are going to Moscow they are again afraid.
"Moscow has some problems financially but as for security there is no problem.
"If the President of the United States can go there, I don't understand why some of their athletes can be concerned."
Johnson, the biggest name in athletics, insisted after he won the 400m in the ISTAF meeting in Berlin's Olympic Stadium last night that he would not be going to Moscow.
The Texan will instead head home to take part in a pro-am golf tournament because he is concerned at the "dangerous" situation in the country following the political and currency crisis.
The IAAF have dismissed calls for the meeting, the richest on the calendar with a total prize fund of about pounds 2.75million, to be switched to another venue.
On the track, Johnson secured another comfortable victory in the 400m, clocking a routine 44.62sec.
Jerome Young, who will face Britain's Iwan Thomas at the World Cup in Johannesburg next week, held Johnson until 300m before seeing him power away in the home straight. Young finished second in 45.18sec with another American Tyree Washington, third in 45 .36.
Two Americans who will be heading for Moscow are Marion Jones and Bryan Bronson, the 400m hurdler.
The duo, along with Morocco's Hicham El Guerrouj and Ethiopia's Haile Gebrselassie, maintained their unbeaten Golden League records in Berlin.
If they all win on Saturday they will each pick up a pounds 250,000 bonus in addition to the prize-money they have collected throughout the season.
But Bronson so nearly missed out by the thickness of his vest on his potential share as he just held off Stephane Diagana, France's world champion, who fell in last month's Europeans.
Bronson won by just 0.01sec while the other three jackpot contenders all had assured victories.
Jones looks a safe bet for claiming part of the bonus as she destroyed her rivals to win the 100m in 10.81sec to stretch her unbeaten record in all events this year to 31.
World champion El Guerrouj won the 1500m by a clear three seconds while Gebrselassie was also a comfortable winner in the 5000m.
Elsewhere, Colin Jackson found avenging American Allen Johnson too strong to handle.
The Welshman, who scored a rare victory over the world and Olympic gold medallist in Glasgow last Sunday, had to settle for second place.
Jackson, who won his third successive European title in Budapest last month, was quickest to the first hurdle where he had a clear advantage over the sluggish Johnson in the lane next to him.
But the American turned on the power in the second half of the race at the to win comfortably in 13.12secs with Jackson clocking 13.20.
The cool conditions kept the times down, but that did not stop a trio dipping under 10sec in the 100m.
Greene set a meeting record of 9.94sec as he made full use of his explosive start with fellow American Jon Drummond second (9.98) with Ato Boldon third in 9.99.
Drummond and Boldon, the Trinidadian who won the world 200m title in Athens last year, have also said they will not compete in Moscow.
There was more joy for Ireland's Mark Carroll as he clocked a national record in the 5000m of 13 minutes 3.93 seconds. Gebrselassie's winning time was 12:56.52.
Carroll, the Cork-born United States-based runner, finished seventh as he followed up his superb bronze medainning effort from the Europeans to slice 10 seconds off his personal best.
Compatriot Sonia O'Sullivan, who scored an historic 5000m-10,000m double in Budapest, found the pace too hot.
O'Sullivan came home fourth in 14:51.61 with Gabriela Szabo, the Romania she outsprinted to win the 5000m title in Hungary, gaining a sliver of consolation with a European record of 14:31.48.
There was also bad news for British triple jumper Julian Golley who was named yesterday as stand-by for the World Cup if world record holder Jonathan Edwards declares himself unfit.
Golley, hoping to defend his Commonwealth Games title later this month, injured himself on his second jump of the competition.
Former world and Olympic champion Linford Christie also made a track appearance, his second in four days, after having retired last year.
Christie, who won the 100m for his club in the Gold Cup Final last Saturday, restricted himself to a spot in the relay. But he was overhauled by a German who a couple of years ago he would have blown away as his Commonwealth quartet finished fifth.