Defending champion Seung-Yul Noh withdrew from the Zurich Classic of New Orleans during the second round, citing a back injury.
Noh shot a 1-over par 73 in the opening round at TPC Louisiana and was even par through eight holes of his second round. He opened with a pair of birdies Friday, but bogeyed Nos. 16 and 17 before deciding to withdraw.
Noh, 23, notched his first PGA Tour victory at this event last year, winning by two shots over Robert Streb and Andrew Svoboda.
Noh has two top-25 finishes in 12 starts this season, with his best result a tie for 11th at the Hyundai Tournament of Champions. His best result in a full-field event came at the Northern Trust Open, where he tied for 22nd, and the Korean missed the cut last week at the RBC Heritage.
Noh was making his 104th career start this week. His lone prior withdrawal came last year at the Shell Houston Open.