DC United goalkeeper Bill Hamid has explained the confusion over his substitution during the USA's failed Olympics qualifier against El Salvador.

El Salvador scored twice with Hamid injured and before he was substituted for Sean Johnson.

"I didn't feel too good," Hamid told the Washington Post. "I tried to test it by jumping, moving side to side, doing some high knee [exercises] right there on the field. Once I did it, there was no doubt in my mind I would do nothing more but hurt the team by staying on.

"They were getting Sean ready. I don't know if you saw [on TV], but Sean was actually getting ready. He was on the line [sideline] before the second goal. The sub was ready to be made.

"The two goals were like three minutes within each other. They didn't wait. [Johnson] was asked to come off the bench and warm up and get ready to come in."