Bayern announced the injury in a statement on Sunday, saying the 29-year-old "tore a muscle in his left thigh during training and is out for the time being".
Portugal play two European Championship fixtures in October, hosting Slovakia on Friday before playing away against Bosnia and Herzegovina four days later.
Guerreiro, who moved from Borussia Dortmund to Bayern in the summer, has only played twice for the German champions due to a different muscle injury, coming off the bench both times.
Defender Matthijs de Ligt and forward Serge Gnabry will also miss the Freiburg match due to injury. Bayern this week considered whether to re-sign centre-back Jerome Boateng due to their defensive injury woes, but announced on Friday that the two-time Champions League winner would not return.
October 8, 2023