Irish charities working on the ground in Port-au-Prince have also expressed concerns about the shock return of "Baby Doc".
John Wain, Haven's country director in Haiti since June, said the response to his arrival was worrying.
"The people here are craving strong leadership, they appear to be happy about his return, however I would be concerned that his presence will only cause further confusion, and add to the air of uncertainty.
The situation was still "extremely confused", with the Organisation of American States recently challenging the preliminary results from the vote.
"Duvalier's arrival will undoubtedly cause even further controversy, but at the moment it is a case of what next? since the November election," he said.