Aardsma has been on the 15-day disabled list all season while recovering from hip labrum surgery.
After getting an MRI on his elbow Saturday, Aardsma was examined Monday by Mariners medical director Dr. Edward Khalfayan, who diagnosed the pitcher with a Grade 2 sprain of the ulnar collateral ligament.
Seattle manager Eric Wedge said Tuesday that the team is certainly concerned.
Aardsma will visit Dr. Lewis Yocum in California on Thursday for a second opinion. After that exam, Dr. Yocum and Dr. Khalfayan will confer and make a recommendation on treatment.
Aardsma had 31 saves last season for Seattle and ranks fourth in team history with 69.