The Spanish keeper is wanted by Villa to solve the injury crisis they are experiencing in that position.
But Reina cannot go to Villa until AC Milan sign a replacement, per the player's agent.
Both clubs are negotiating, but Villa know that Milan will not sell unless they are confident of securing another keeper themselves.
"No, there's no agreement," the player's agent Manuel Garcia Quilon told Sky Sport Italia.
"We continue to negotiate, but the Rossoneri would like to bring in a replacement first."