The 36-year-old defender announced on Monday that he will move on at the end of the season after more than two decades at Stamford Bridge.
"It came as a surprise," Fabregas told talkSPORT. "There was a lot of talk and speculation that it could be his last year but we didn't know for sure.
"It is a very personal decision between him and the club. It is a shame because I cannot see anyone replacing the role he does in the team. He is irreplaceable for now."
Terry is Chelsea's most decorated player of all time having won the Champions League, four Premier League titles, the Europa League, five FA Cups and three League Cups.