Russia defeated Serbia 2- 1 in a friendly international Wednesday but lost striker Pavel Pogrebnyak to a knee injury, the dpa reported.
Russia's Dutch coach Guus Hiddink said he feared the Zenit St Petersburg forward had suffered a torn ligament which would put him out of the European Championships starting on June 7.
"We are really concerned," Hiddink said, adding that an examination on Thursday will reveal the extent of the injury.
Pogrebnyak had put Russia in front in the 12th minute of the match in the German town of Burghausen, but suffered the injury three minutes later.
Spartak Moscow's Roman Pavlyuchenko came on for Pogrebnyak to score the 48th-minute winner for Russia after Marko Pantelic had equalized for Serbia five minutes before half-time.
The victory comes five days after a 6-0 win over Kazakhstan. A last test for Hiddink's side before Euro 2008 follows next Wednesday in Burghausen against Lithuania.
Russia's group opponents at the June7-29 tournament in Austria and Switzerland are Spain, title-holders Greece and Sweden.
Serbia, who did not qualify for Euro 2008, come up against Germany on Saturday in Gelsenkirchen.