He has struggled to establish himself as a first choice at Valencia and is continuing to be the subject of speculation during the January transfer window.
Zigic's representative Milan Calasan says Chelsea and Liverpool are now showing an interest, along with clubs from Germany and Italy.
"In recent time, Nikola has received much more playing time and uses it quite effectively, but it is still not enough for his potential," Calasan told Futbol Mercado. "At the moment he is followed by Chelsea, Liverpool, a couple of German clubs and one Italian club.
"If an offer comes in, we will definitely take it into serious account."
However, Zigic has expressed his determination to make an impact at Valencia after recently rejecting the chance to join Russian outfit Zenit St Petersburg.
Zigic told Sportal: "Only time will show how my stance will change in the plans of the coach (Unai) Emery. My opinion is that it will not change much.
"I refused Zenit's offer as I don't want to go to Russia, but it doesn't mean that I am ruling out the possibility of changing clubs.
"At the moment, I would prefer to stay at Valencia and to fight for my place in the team as I have two-and-a-half years still on my contract."
La Liga 2009/10 Win Outright: Valencia 25/1