Only four days remain until Sweden's World Cup debut against Tunisia, and wingback Gudmundsson's participation appears even more uncertain.
Gudmundsson was unable to train on Tuesday and is now missing a second straight training session.
Is he isolated?
"He is keeping to himself, as one should when feeling unwell. He has mild symptoms," Thorén told Swedish journalists on site in Dallas.
Sweden's World Cup opener against Tunisia will be played on Monday night in Monterrey, Mexico.
