He did get a red card when he came on. Which was bull$#@!. $#@!ing Ramos
But you are right. Even if he was in poor form, he should have been subbed on for Barzagli at the half, and Alves moved back to RB. It was obvious even during our good first half performance, that Barza wasn't up to being on the flank facing Real Madrid's front line.