Dr. Oz says he wants to help Sterling Shepard figure out what's wrong with his brain ... but he's warning the New York Giants star retirement might be his recommendation.
Sterling has been held out of Big Blue's last four games because of complications with a concussion ... and his head coach, Pat Shurmur, just called it a "serious injury" this week.
When we got Dr. Oz out in NYC on Thursday ... he offered to lend the receiver a hand -- saying he wants to conduct some tests on the 26-year-old to see if he's legitimately okay.