The Ecuadorian's one-month contract expired this week with his only appearance for the Blues to date coming off the bench in the 2-0 win at Doncaster.
McLeish told the club's official website: "I'm still speaking to Ulises because he's undecided about going back to Ecuador.
"He still harbours ambitions of getting to the World Cup.
"I know that may be a long shot for Ecuador in terms of their position in the South American qualifying campaign. But the other campaign he's targeting is the Copa America.
"These are issues I'm talking to him about."