Gunnell, her face drawn and traumatised beneath the tan that she normally has at this time of the year, explained afterwards that the problem was in her left leg - not the one which required a heel operation shortly before last Christmas.
She will travel to the Swiss sports science centre at Magglingen, 100 miles from Lausanne, today to consult with the doctor - Rolf Biedert - who carried out that operation, removing a bone spur which was pressing on the bursa in her heel. That injury kept her out of hurdling for 20 months.
Last night she was clearly confused by the sudden turn of events which left her facing the possibility of further surgery, although she strove to prevent her fears running away with her.
"If it does need another operation I don't think I could go through with it," she said. "But I may just be panicking myself. It is exactly the same kind of pain I felt in the other leg. I felt it sharply just as I was coming off the sixth hurdle. I was going quite well... and then that happens. I can't believe it."
She said that she had been troubled by her leg for two weeks, and had asked a physiotherapist to accompany her as a precaution so the leg could be checked over after her race.
"I felt it quite a lot in the warm-up," she said. "But, you know, you want to run."
This was to have been the Olympic champion's showdown against the two Americans who ran inside her world record at last year's World Championships. In the event, Tonia Buford, the silver medallist in Gothenburg, won in 53.61sec ahead of the champion, Kim Batten.
But the main drama resided in the scene being played out on the final bend, as Gunnell's husband, Jon Bigg, raced over to comfort her. It was a shattering conclusion to a race where she hoped to re-establish herself as a medal contender.
Did she, someone asked, expect to be able to go to Atlanta now. "I bloody well hope so," she said defiantly. But the strain on her face was painful to behold.
Earlier this week Buford had claimed that the event was "passing Gunnell by". But she certainly would not have envisaged it happening so cruelly and so literally last night. Linford Christie, named as British Olympic captain alongside Gunnell, commented: "It's such a shame for her, she was coming back so well."
Michael Johnson's awesome sprinting form produced another record here in the 400m - not for himself, but for Roger Black, who lowered his own British mark to 44.37 as he strained in the Texan's wake.
Johnson, who broke the 24-year-old world 200m mark last month, began slowly and finished fast to win in 43.66, 0.37sec outside Butch Reynolds's eight-year-old world mark.
The world record which came closest to being broken was that for the 100m, where Frankie Fredericks recorded 9.86, just 0.01sec off the record Leroy Burrell set on the same track two years ago.
Among those he defeated in a field assembled at a cost of $250,000, was the world champion, Donovan Bailey, and Fredericks' sometime training partner Linford Christie, whose mind will have been concentrated wonderfully for the Olympic task ahead by finishing fifth in 10.04.
But for the celebratory raising of his arms as he crossed the line, Fredericks, who had already recorded 9.87 this season, might have taken the 100m record. Bailey eventually finished second in 9.93, with Boldon third in 9.94 and Jon Drummond fourth in 10.00.
Christie's immediate reaction was to smile ruefully and offer his applause to his friend, who was already cavorting towards the crowd firing imaginary pistols in the jubilant style of, well, Linford Christie.
Britain's Olympic champion finished his evening by finishing second to Boldon in a 200m which the Trinidadian won impressively in 19.85, despite easing down over the last 10 metres. It is becoming very clear that Christie's decision to compete in Atlanta was not a simple one.
Colin Jackson also had his Olympic ambitions put into perspective. Jackson succumbed to a stronger finish from the American 110m hurdles world champion, Allen Johnson, who came within 0.01sec of his world record of 12.91 last month.
Johnson won in 13.08, but the Welshman, who has recently shaken off the worst effects of tendinitis in his knee, was relatively cheered by his performance in coming second in 13.13 despite what he described as "scrappy" hurdling. "It was still a good run to get so close to Allen considering he was coming off the back of 12.92," Jackson said.
Black's time, which bettered the record he set in winning last month's Olympic trials by 0.02sec, confirmed him as the leading British one-lap runner going into the Games.
"I haven't been feeling too good in myself so I'm surprised I'm running so fast," Black said. "But it's good to be running 44's consistently. There can't be much wrong with me if I'm running like that. Consistency. That's the key to this game.
"I was leading after 300 metres and I was thinking, where the hell is he? I didn't have to wait for long. When Michael Johnson is running it is a fact that there are always two races. He is way ahead. But at least I won the second race."
It was another outstanding night for British 400m running following last month's Olympic trials, which saw four home runners go under 45sec in a single race for the first time.
Iwan Thomas, who has an individual place alongside Black in Atlanta, was sixth here in 44.71, a best for him at sea level. Just over an hour earlier, two Britons who have had to settle for relay places in Atlanta established themselves as the fourth and fifth fastest Britons of all time. In a B race won by America's Anthuan Maybank in 44.15, Mark Richardson was second in 44.52, and Jamie Baulch third in 44.57.
Results, Sporting Digest, page 30