The U.S. entry in the 4 x 400-meter relay team at this summer's Olympic Games has not yet been set, but one name has officially been eliminated from contention.

Debbie Dunn, who finished fourth in the 400 at the U.S. Olympic trials in Eugene, Ore., has withdrawn from the relay pool for this summer's Games after testing positive for the "likely presence" of an anabolic steroid.

"I do not want any issue like this to distract from my teammates' focus for the biggest meet of their lives," Dunn said in a statement to the Chicago Tribune, which first reported the test. "I wish Team USA best in London as I work toward resolving this matter."

The USADA is currently testing the "B" sample that Dunn gave at the trials (all athletes give two samples in the event of a positive test), and USADA chief executive Travis Tygart said that "as in all cases all athletes are innocent until and unless proven otherwise through the established full, fair legal process which was approved by the athletes, the U.S. Olympic Committee and all Olympic sports organizations.

The 34-year-old Dunn, born in Kingston, Jamaica, resides in Norfolk, Virginia. She was on the Olympic team list released earlier this week by the USOC.  She won the US outdoor title in the 400 in 2010 with a time of 49.64 seconds.

It has not yet been determined whether the U.S. can replace Dunn on the Olympic team.