Napoli are reported to be wanting close to £90million to part with the Senegalese defender, who was heavily linked with an Old Trafford switch in January.
"My future? I don't know if I'm one of the strongest defenders. I always try to give my best," Koulibaly told Rai Sport on Friday.
"Since I'm here, I always try to grow with Napoli. I have a lot of motivation to go on and I want to keep doing this.
"I am pleased that many teams follow me, but I want to demonstrate on the field that I am at the level of the greatest and I want to show it in the future."