The defender sustained the injury in last week's away win at Benfica and, despite completing that game and all 90 minutes of Saturday's Premier League win at Aston Villa, he was forced off after an hour yesterday.
He said: "It's just horrible. When you get one in the ribs, you can't do anything about it, you can't treat it, you just have let it heal, but I can get through games definitely.
"I thought it was OK but, later in the second half, it just seemed to be getting worse and I was struggling to breathe to be honest.
"It was difficult. I have never felt anything like that before."
Terry revealed he would undergo a scan this morning, with Chelsea this afternoon confirming their skipper's diagnosis.
Chelsea can ill-afford to be without the 31-year-old for too much of what is a nightmare run of eight games in 26 days.
But caretaker manager Roberto Di Matteo looks certain to rest him for Saturday's visit of Wigan, with Easter Monday's west London derby at Fulham also to consider.
It is unthinkable Chelsea would do anything to jeopardise their captain's chances of being fit for Barca.
They struggled badly during his absence with a knee injury earlier this year and their remarkable turnaround in fortunes Di Matteo coincided with Terry's return.
Last night's unconvincing win was their seventh success in nine matches since Di Matteo took charge and Terry was bullish about beating an all-conquering Barca side many people already have nailed on to retain their European title.
He said: "It's a very good achievement to reach our sixth semi-final in nine years, but we want to go through to the end.
"Clearly, that's going to be tough against Barcelona, but we're playing well.
"I am not sure anyone will fancy playing us at the moment because we are a very good side, especially in this competition.
"Barcelona are a very good team but, home and away, we're a very solid side as well.
"We have shown that away against a very good Benfica side and proved on big nights at Stamford Bridge that we can really upset teams as well.
"We're confident. It is important we keep this momentum because we're going well in the league. That is the key for us."
Frank Lampard last night admitted Chelsea had "unfinished business" against Barca after 2009's penalty controversies and no one has more reason for revenge than Didier Drogba, who served a three-match ban for his furious complaints about the referee after that tie.
The striker said: "The Chelsea team is different but, if we have the same mentality, we can create new problems.
"Every game is different and I hope we can beat them to go through.
"Reaching a sixth semi-final shows how consistent Chelsea have been in the last 10 years in the competition, but winning it is what matters.
"It's going to be difficult but I hope we beat Barcelona and can be in the final again."
Winger Juan Mata will play his first Chelsea-Barcelona clash but he knows all about the Catalans from his time at Valencia.
The summer signing said: "Barcelona have most of the best players in the world but we are Chelsea and we will fight.
"Are they beatable? In football nothing is impossible."
Striker Salomon Kalou, who was on the bench in 2009, said: "Barcelona is a hard game but not impossible.
"We respect them because they are a great team with great players but it's a Champions League semi-final and you never know.
"We have to believe we can do it."