The 26-year-old centre-back joined the Premier League club on a free transfer last summer from Lazio, but has failed to feature regularly for the Black Cats so far this season.
Diakite has played only seven times in the league and once in the FA Cup, leading to suggestions that he could be let go if a suitable offer comes in.
Italian club Fiorentina could now make a bid for the Frenchman, although the Viola insist that they are still unsure about it.
"Diakite is one of the players that we are evaluating, but our situation is calm and it is not certain that we will sign a defender," Prade told reporters.
When asked about AC Milan centre-back, Philippe Mexes, Prade said: "He is a strong player but he's not in our plans."