Bayern Munich sporting director Matthias Sammer has questioned referee Carlos Velasco Carballo's failure to hand a second yellow card to Manchester United winger Antonio Valencia at Old Trafford on Tuesday evening.
Valencia was fortunate to escape after sliding in late on Jerome Boateng, and after Bayern midfielder Bastian Schweinsteiger was later dismissed for a second booking, Sammer has insisted that the "same standards" were not applied.
The 46-year-old told Sky Germany: "If you apply the same standards, then I don't know how Valencia stays on. If the referee has a policy, then he must go through with it.
"There's no question that what Schweinsteiger did was a foul, but with Valencia, there were also several fouls and his outstretched leg against Jerome Boateng. At this level, you have to apply the same standards."
The first leg in Manchester ended in a 1-1 draw, with Schweinsteiger cancelling out Nemanja Vidic's opener for United.
