"This is an MRI of my hamstring," Foster wrote. "The white stuff surrounding the muscle is known in the medical world as anti-awesomeness."
Foster, the NFL's reigning rushing champion, re-signed with Houston before the preseason but aggravated his hamstring during Saturday's preseason contest against the 49ers.
It's not known how long the injury could keep Foster out of action, but a sports medicine expert at ESPN said it was significant and that the MRI "demonstrates considerable muscle damage with bleeding and swelling."
Dr. Michael Kaplan told ESPN that he believed Foster wouldn't be able to return to the field for three to four weeks, but Foster had other ideas.
"If I had a "significant injury" why post it?," he tweeted. "I'll be fine, it was jus meant to make fun of the whole situation. Humor is lost nowadays."
Foster, who had arthroscopic surgery on his right knee in the offseason, burst onto the scene in 2010 -- his second year in the league -- and totaled 2,220 yards from scrimmage, including a league-leading 1,616 rushing yards, to go with 18 touchdowns.