"This is something that's going to get out," Foster told NFL.com on Thursday. "I don't make excuses. I'm a real dude. I try to be a good person. ... I just hope the coaches understand and that's all I can hope and pray for."
Under provisions of the NFL's substance abuse policy, a diluted sample is treated like a positive test.
Foster told NFL.com that the positive test came after he tried to rehydrate himself after coming down with what he believed to be food poisoning. He said that, before the combine, he had been vomiting, cramping and suffering from diarrhea, and that he declined IVs and instead got medication from a doctor.
"I couldn't eat much, but I had to drink water and Gatorade," Foster told NFL.com. "Then a few coaches said something about me being too light. And I'm a coach-pleaser. I don't care what everybody thinks, but I care what coaches think. So I drank and ate as much as I could without throwing up. Then I went in there, drinking and drinking water, trying to flush out my system from whatever was making me sick and trying to keep my weight up and took the test."
Foster, once regarded as a potential top-10 pick in the NFL draft, was sent home from the combine after a "heated altercation" with a hospital worker, sources told ESPN on March 4. The NFL at the time would only say that it was for "personal reasons."
In their latest two-round mock draft, ESPN NFL draft Insiders Mel Kiper Jr. and Todd McShay project Foster to be selected at the Nos. 15 and 17 spots, respectively.
Foster was Alabama's leading tackler last season and a unanimous first-team All-American. He also won the Butkus Award, given to the nation's best linebacker.
He had rotator cuff surgery in his right shoulder after the season and was projected to be fully recovered by the start of NFL training camps.