Arsenal have been credited with an interest in Mignolet with Gunners boss Arsene Wenger thought to be in the market for a new keeper this summer.
Mignolet has enjoyed a fine season for the Black Cats despite their struggles at the wrong end of the table and N'Diaye can understand why the Belgian international is attracting interest from other clubs.
"Simon is a quality keeper. When I came here I had not seen him or heard of him, but every time he plays he is fantastic. The quality is there for all to see," said N'Diaye.
"I can understand why he has been linked with other teams because this is normal. It is very normal for that to happen when you play as well as he does.
"He is better than the keeper at Arsenal, Szczesny, he is better than him - no doubt about it.
"Mignolet was brilliant against Southampton and he is like that every week. He is such a good keeper and that is why he is being linked with other clubs."