Germany midfielder Sami Khedira is a doubt for their World Cup qualifiers against the Czech Republic and Norway, the team said on Wednesday.
The 30-year-old missed the world champions' morning training session and will undergo medical checks on Wednesday after complaining about pain in his knee.
"We will have to wait until after the medical examinations later today," a team spokesman said.
The Juventus player was not part of Germany's Confederations Cup-winning team in July, having been rested by coach Joachim Loew ahead of next year's World Cup in Russia.
Loew is already without winger Serge Gnabry, who left the team hotel on Tuesday with an ankle injury.
Germany, who top Group C, take on the Czechs in Prague on Friday before hosting Norway in Stuttgart three days later.
They have a maximum 18 points from six games, five ahead of second-placed Northern Ireland and nine in front of the third-placed Czechs.
(For more sports news and updates, follow Ahram Online Sports on Twitter at @AO_Sports and on Facebook at AhramOnlineSports.)