The German midfielder picked up the knock on his right foot during a practice session in preparation for their clash with Chivas Guadalajara and will now have scansReal Madrid midfielder Sami Khedira has been forced to withdraw from training after sustaining a metatarsal injury on his fifth right toe.
The former Stuttgart man left the session just before its completion, complaining of severe pain in his right foot, according to EFE.
After being monitored at the Ronald Reagan Medical Center in Los Angeles, near the club's training base, more tests will be conducted on Wednesday afternoon to confirm the extent of the setback.
Khedira has experienced a number of knocks in the past, and was limited to 25 La Liga games in 2010-11 after battling injuries throughout the campaign.
Jose Mourinho's men travel on Wednesday morning to San Diego in California, where they will face Mexican side Chivas de Guadalajara.