Daltrey was struggling with 'Who Are You' and Townshend eventually picked up the lead vocals. After that, the band played 'Eminence Front' with Townshend leading the vocals.
Daltrey then addressed the crowd, "I think I should quit while I'm ahead," and walked off stage. After a while, Townshend came back onstage to break the unfortunate news to the audience.
"I'm really, really sorry," he said. "Roger cannot actually speak now. Apparently, before the show he saw a doctor, and, you know, he's been singing so fucking great through this tour. I don't know what the fuck's going on. He has been on top of his game."
Townshend also added that there was no point trying to make a new set without Roger because "this is Roger's show, really. It's a vocal show, and he's not in good shape."
The Who has yet to release an official statement about the status of Daltrey's voice or if they are postponing their next show in Dallas.
Recently the band has released their first new album in 13 years, see the details here.