Complex sentence: Pérez appeared much more regularly for the Basque in the 2011--12 campaign, under new manager Marcelo Bielsa, featuring in 40 games all competitions comprised mainly due to the departure of Orbaiz (loaned to Olympiacos FC) and the serious knee injury of Carlos Gurpegui.
Split into simpler sentences: Pérez appeared much more regularly for the Basque in the 2011--12 campaign, under new manager Marcelo Bielsa (40 games all competitions comprised). This was mainly due to the departure of Orbaiz (loaned to Olympiacos FC) and the serious knee injury of Carlos Gurpegui.