The 24-year-old missed Saturday's goalless draw at Villarreal with a thigh strain and will reportedly not recover in time for the first leg of the semi-finals at Mestalla.
It is also reported that Pedro's availability for the La Liga visit of Real Sociedad on February 5 is in doubt.
The news comes as the latest worry to coach Pep Guardiola, who will have to find more room on the crowded Blaugrana treatment table, as Ibrahim Afellay, Andreu Fontas, David Villa and Andres Iniesta are all unavailable.
The Copa del Rey match at Mestalla will kick off at 21.00CET.
Starting in November and continuing through to the middle of February, Goal.com is publishing exclusive extracts from Graham Hunter's highly-anticipated new book, 'Barca: The Making of the Greatest Team in the World'. Friday's extract looked at how Barca suffered rare disappointment at the hands of Real Madrid in a gripping finale to last season's Copa del Rey. Don't miss it!