Klein posted an old picture of himself beneath a photo of 15-year-old Prince Michael with the cryptic tag 'hmmmmm'.
The photo appears to be a wry nod to conspiracy theorists who have speculated for years that Klein donated his own sperm to help the late King of Pop start a family.
Jackson, who died in 2009, fathered Prince Michael and daughter Paris with ex-wife Debbie Rowe, who previously worked as Klein's assistant at his practice in Beverly Hills.
Jackson's third child Blanket was born by an anonymous surrogate in 2002.
Rowe has never spoken publicly about the identity of the biological father of the children she bore Jackson.
However, Klein has previously gone on record to rule out any role in the parenting of Jackson's children.
"To the best of my knowledge I am not the father of these children," said Klein, who has fallen on hard times since the days when he boasted a celebrity clientele which included some of Hollywood's biggest names.