"As I was stepping away he continued to swing and caught me flush on the elbow"
The Dubliner suffered an elbow injury which occurred when he was out on the range coaching an amateur.
"Yesterday I picked up an elbow injury at a golf outing in Washington DC," the three-time major winner wrote on his personal website.
"Whilst coaching an amateur golfer on how to cure his hook, I stepped in close to demonstrate the action for a fade, but as I was stepping away he continued to swing and caught me flush on the elbow.
"My initial thought was that the elbow was shattered and it was the end to my competitive playing career. I nearly fainted with the pain and shock.
"I applied ice to the elbow within seconds and also compressed it to minimise any inflammation. After an X-ray at the hospital I was delighted to learn that it wasn't broken, but it still required 6 deep stitches.
"I have been advised to be cautious and it will need 10-12 days for the stitches to heal, so I have been forced to withdraw from this week's FedEx St Jude Classic tournament in Memphis."
Harrington will miss next weeks US Open at Erin Hills having failed to qualify through a qualifier at Walton Heath last week. Rory McIlroy, Shane Lowry, Graeme McDowell and Paul Dunne have already qualified.
Larne amateur Stephen Watts and West Waterford's PGA Tour star Seamus Power will bid for US Open places at Sectional Qualifying on Monday.
Ironic that a potential injury caused coaching an am could of resulted in me becoming a full time coach.— Padraig Harrington (@padraig_h) June 6, 2017
I'll only be out for 12 days or so to let stitches heal.— Padraig Harrington (@padraig_h) June 6, 2017