The 35-year-old was handed a one-month contract with Blues back at the start of March having impressed as a free agent while on trial when the club were struggling with injuries.
His month-long deal expired last week having made just one substitute appearance at Doncaster. And although manager Alex McLeish had offered him a contract until the end of the season, he has opted to turn it down with almost all of the club's previously injured defenders now back in action and vying for first-team action.
McLeish said in the Birmingham Mail: "I did give him the opportunity to stay to the death with us, but he declined.
"I think he will be going back to Ecuador to give himself the best chance of being involved with the national team for the World Cup and Copa America campaign.
"We could have gone with him, even though Stephen Carr is playing great and we've got other players back and available."