According to the facebook of Lamb Of God, drummer Chris Adler sits out the upcoming US tour.
Here is the official statement
“Due to unforeseen circumstances, we regret to inform you that Chris Adler will not be performing on our upcoming North American tour with Slayer. In his absence, we would like to welcome Art Cruz, who will be filling in at the recommendation of Chris. We expect to see Chris returning in the very near future. We will see you all on the road soon.”