The movie actor landed a part in the crime drama in 2008, replacing series regular William Petersen.
Last summer (09), reports suggested TV bosses were keen to bring back Peterson to make a cameo as forensics expert Gil Grissom in a bid to boost falling ratings.
A source said, "The bottom line is that CSI just hasn't been the same without Grissom. He's the show's heart and soul. When Grissom left at the end of the ninth season... a lot of longtime viewers went with him.
"There was a brief ratings bump when Laurence Fishburne joined the cast at the beginning of last season, but the numbers have gone downhill ever since."
CSI: Crime Scene Investigation has averaged 15.9 million viewers in the U.S. this year (10), a drop from the 18.8 million its ninth season attracted last season (09), according to the Hollywood Reporter.
But TV bosses are standing by their man and have signed Fishburne up for another season, keeping his character, Dr. Raymond Langston, on the show until 2011.