The influential Brazilian's problem is the latest in a long line at Serie A leaders Milan and striker Zlatan Ibrahimovic told reporters that "something has to change" within the club to stop the injuries.
Thiago Silva was not fully fit for Saturday's 2-1 win at home to AS Roma and came off after just 11 minutes as coach Massimiliano Allegri's decision to play him backfired.
He left the San Siro on crutches.
"I decided to risk him today and this is how it went," Allegri told reporters.
"I willingly took the risk because today's match was fundamental for the Serie A championship. And we will now pay dearly for it. He has a problem to his right thigh flexor muscle, I think it is virtually impossible for him to play on Wednesday."
Daniele Bonera could deputise again at centre half against holders Barca with Alessandro Nesta not 100 percent fit.
Top Italian sides, once renowned for having the best medical teams in Europe and lauded by Manchester City's Italian manager Roberto Mancini this week, have struggled with injuries in recent years.
Inter Milan had a raft of fitness problems during Rafa Benitez's tenure in 2010 with pundits blaming his training regime while reports said humidity at Juventus' Vinovo base was behind their slew of injuries several seasons ago.