Thomas, testifying Wednesday in a Castle Rock court, said Cox carried the unconscious woman to a bedroom in his Lone Tree home during Labor Day weekend 2010 only to return to the living room to tell Thomas, "I think she's ready," The Denver Post reported.
Thomas, who said he had been making out with the woman earlier, said he believed Cox meant the woman was ready to have sex with him.
Thomas said he replied to Cox, "Nah, I don't think so," adding, "I don't know what (Cox) did after I left."
Prosecutors allege Cox then had sex with the victim, who became pregnant with Cox's child, DNA tests show.
Cox is charged with two counts of sexually assaulting a helpless victim unable to appraise her own condition and faces up to life in prison if convicted, the newspaper said.
The victim testified Tuesday and Wednesday she believes she may have been drugged because she had no more than four drinks.
The defense has not yet presented its case.