Per Chargers.com, there wasn’t any other information on the injury.
A strain is an injury to a tendon or muscle, not a ligament.
The Chargers’ top wide receiver in 2012, the 31-year-old Floyd was injured in practice earlier on Monday and was taken off the field via cart.
Update: The Chargers breathed a sigh of relief on Monday when they learned that wide receiver Malcolm Floyd has a knee strain rather than a torn ACL, but it still may be some time before he’s able to return to the lineup. Read more 
Source: Mike Wilkening, NBC Sports Pro Football Talk