Law enforcement officials spoke to Sergey Malinka, who was questioned as a witness in 2007 after the child's disappearance from a Portuguese resort.
The second suspect's name wasn't reported. The two men were released after the questioning at a police station in Faro.
Two other people of interest were to be questioned as well, including a person who suffered from schizophrenia. All four are Portuguese citizens.
McCann disappeared in 2007 while on vacation in Portugal with her family. Her parents had left her sleeping at their room at the Praia da Luz resort to eat at a nearby apartment and when they returned she was gone.