The other 25 players in Sweden's World Cup squad took part in the training session, which was held in front of a couple of thousand spectators.
The national team opened its doors, and the response was great.
How serious Gudmundsson's condition is remains unclear, but if he falls ill and misses the World Cup opener against Tunisia in Monterrey early Monday morning, local time in Sweden, it would be a major setback for the Swedish defense.
The wingback is, if he is healthy and fit, a given in national team coach Graham Potter's starting eleven. Gudmundsson returned against Greece last week after an injury layoff of more than a month.
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