Jupp Heynckes has a major decision to make when his Bayern Munich side visit Camp Nou, with six of his players just one booking away from suspension
Mario Gomez, Bastian Schweinsteiger and Javi Martinez all picked up cautions during the Bavarians' 4-0 demolition of the Blaugrana at the Allianz Arena, leaving all three walking a tightrope on Wednesday.
Brazilian duo Dante and Luiz Gustavo also sit on two bookings, as does captain Philipp Lahm after he received a yellow card in each leg of his side’s round of 16 victory over Arsenal.
Barcelona’s defensive problems could be further exacerbated should Gerard Pique mistime a challenge as the Catalans go all out to come back from the brink. Alex Song also runs the risk of a suspension after he was twice booked during the group stage.
Jurgen Klopp has little to worry about when Borussia Dortmund visit the Bernebeau on Tuesday, with only Kevin Grosskreutz one card away from missing a potential final.
Real Madrid coach Jose Mourinho, meanwhile, will have to try and curb the enthusiasm of Sergio Ramos and Michael Essien, both of whom carry two previous bookings into the clash.