CHARLOTTE, N.C. -- Vijay Singh, who earlier this year admitted to taking a banned substance, will not face any sanctions after the World Anti-Doping Agency determined that the use of deer-antler spray is no long considered prohibitive.

Singh, 50, who has three major championships among his 34 PGA Tour victories and is a member of the World Golf Hall of Fame, was told by commissioner Tim Finchem on Tuesday before a practice round at the Wells Fargo Championship that he had been cleared of any doping violations.

On Wednesday, Singh withdrew from this weekend's Wells Fargo Championship at Quail Hollow in Charlotte, N.C., citing a back injury, PGA Tour officials said. He was replaced in the field by Andrew Svoboda.

Finchem said during a news conference on Tuesday at Quail Hollow Golf Club that Singh had been sanctioned in February, with his case under appeal. The case was dropped, Finchem said, due to WADA's findings.

After conducting tests on the product Singh admitted to taking, WADA determined that it no longer considers the use of deer-antler spray to be prohibited unless there is a positive test result.

Singh did not test positive for IGF-1 -- the Tour has no test for it -- a banned substance found in deer-antler spray. He admitted taking it, which by the Tour's rules is treated the same as a positive test.

"Based on this new information, and given WADA's lead role in interpreting the prohibited list, the Tour deemed it only fair to no longer treat Mr. Singh's use of deer-antler spray as a violation of the Tour's anti-doping program,'' Finchem said.

Singh first admitted to taking the supplement in a Jan. 28 story that appeared on SI.com. He said at the time he was not aware it might contain IGF-1, a growth factor that is listed on both the WADA and PGA Tour prohibited lists.

The Tour had warned its players about deer-antler spray in August 2011, but there is no test available in routine blood testing. At this time, the Tour only conducts random urine tests. But an admission is still a violation of the policy, and Finchem said a sanction was issued to Singh on Feb. 19.