The 23-year-old, who emerged as one of Leverkusen's most important players in the first half of the season, limped out of training after pulling a muscle.
He will undergo a scan to confirm the extent of the damage, but coach Robin Dutt has warned he could be out of Leverkusen's first game of 2012 against Mainz on January 22.
"It is definitely going to take one or two weeks before Sam is fit again," he said on his club's website.
"But we have not complained (about injuries) so far so we are not going to start now."
Stefan Reinartz was also unable to train on Friday, but he was left out only as a precaution and he should be back in action in the next few days.