The most humiliating moment was being hauled off in a Champions League semi-final against his former club while Barca were trailing .
Guardiola sending Gerard Pique -- who would go on to score -- up front in his place .
The most humiliating moment was being hauled off in a Champions League semi-final against his former club while Barca were trailing , and Guardiola sending Gerard Pique -- who would go on to score -- up front in his place .