Kicked-to-the-curb Brad Pitt has more than just his failed marriage to worry about — pals fear the Fight Club stud could be suffering from a devastating mystery illness!

The 52-year-old actor appeared to be seeing a top infectious disease specialist in Beverly Hills, sources told Breaking Celebrity News.

"Brad arrives at the medical building very early in the morning," a source revealed.

"It's before the office opens to receive other patients, likely so Brad won't be recognized or seen by anyone. He comes in by 7:30 a.m and a staffer lets him in."