The 24-year-old Frenchman spent the second half of last season on loan at Betis after failing to force his way into Black Cats boss Gus Poyet's plans, having already headed out to Turkish side Eskisehirspor with predecessor Paolo di Canio similarly unimpressed.
He is available as the head coach and sporting director Lee Congerton work to reshape the squad, but amid reports that the Spaniards are about to clinch a £1.5million deal, Velazquez was giving little away.
Asked about N'Diaye and speculation that Fiorentina midfielder Joaquin could return to his former club, the coach told the club's official website, www.realbetisbalompie.es: "There is constant communication between the technical secretariat and the coach
It also happens between the board of directors and myself.
"We maintain an ongoing relationship over different situations
These are internal issues.
"I find two great players, each with a different profile
From there, if there are options or not is an internal matter, and it should stay so."
N'Diaye was signed by former Sunderland boss Martin O'Neill for around £3.7million from Bursaspor in January 2013 and despite making a favourable early impression with the club's fans, has made only 16 senior appearances.
Sunderland are currently pursuing their interest in Fiorentina defender Marcos Alonso, who spent the second half of last season on loan at the Stadium of Light, while striker Ignacio Scocco is wanted by former club Newell's Old Boys after an unproductive few months on Wearside following his January move from Internacional.
Source : PA
Source: PA