The Blues failed to land the Croatian player during the summer and Spurs are now offering him improved terms.
Former Chelsea player-coach Gullit believes that Andre Villas-Boas's team would be boosted by the 26-year-old.
"The player Chelsea still need, for me, is Modric," Gullit said.
"They have great players all around the pitch but he has something Chelsea doesn't have at the moment. He is creative and dominates the passing game in the midfield - he could be like Xavi or Iniesta are to Barcelona.
"I was surprised Tottenham didn't accept £40m because they are known to sell their best players for good offers. I think Chelsea will try to sign Modric again in January and maybe this time they will get him."
Gullit is currently in charge of Russian Premier League club FC Terek Grozny.