The 26-year-old Bayern München star injured her left knee when she blocked a Polish giant chance at the end of the first half and stopped the attack by Ewa Pajor.
Gwinn received treatment, came back, but sat down fairly quickly in the grass and was helped off the pitch in tears.
Gwinn missed the World Championship 2023 with a cruciate ligament injury – how serious it is this time remains to be seen.
Germany, eight-time European Championship winner, is chasing its first international title since the Olympic Games gold in Rio 2016 when Sweden was defeated in the final.
European Championship debutant Poland – Sweden's next opponent on Tuesday – held out for just over a half.
Then Jule Brand scored with a dream goal in the 52nd minute when she precisely outside the penalty area curled in 1–0 in the far corner.
The German dominance increased as the match progressed and the chances followed each other.
Lea Schüller could head in 2–0 in the 66th minute.
Sweden meets Germany in the last group stage match on July 12.
