Mangane, 29, has joined on loan from Saudi Arabian side Al-Hilal for an initial cost of €300,000, with the Black Cats holding the option to make the deal permanent in the summer for €3 million.
And O’Neill is certain his arrival will bring some much-needed power and physicality to the team.
“Kader is player who will add to the overall strength of our squad and give us options,” the Irishman told ESPN.
“He will improve competition for places and we are delighted to welcome him to the club.”
Meanwhile, midfielder N’Diaye has arrived at the Stadium of Light from Turkish club Bursaspor on a three-and-a-half-year deal for an undisclosed fee.
Earlier, O’Neill revealed the signings of N’Diaye and Mangane are part of a concerted effort to add height and power to his Sunderland squad. N’Diaye, 22, stands at 6′ 2”, while Senegalese defender Mangane is 6′ 5”, and O’Neill admitted earlier in the season that, without club captain Lee Cattermole in the side, Sunderland lacked a certain physicality.
“Alfred coming in, it’s not just absolutely and utterly to do with the size aspect of things,” he said. “I think he has the talent and the energy as well and I think he could be a really decent hit here.
“The reality is we are a bit small as a squad, maybe the smallest in the Premier League, and we had problems with the physical aspect in some games earlier in the season.”