Cardinals coach Bruce Arians told reporters today that linebacker Deone Bucannon recently had ankle surgery (Twitter link via Ian Rapoport of NFL.com). Bucannon is a PUP candidate as a result, but the team hopes that he will be back by early September. 
Bucannon, 25 in August, played primarily at linebacker in 2016 after trying his hand at strong safety in the previous two campaigns. All in all, he registered 89 total tackles, two pass deflections, and one fumble recovery in 13 games before his troublesome ankle shut him down in December. The former first-round pick was ranked as the No. 34 linebacker in the NFL by Pro Football Focus at the time of his injury, a score that was boosted a his exceptional 86.1 coverage score.
If the Cardinals are without Bucannon for an extended period of time, they may want to look into adding an experienced inside linebacker. Free agent pickup Karlos Dansby will hold down one ILB spot, but the only other true ILBs on the roster are journeyman Zaviar Gooden and former University of Arizona standout Scooby Wright. Alternatively, if the Cardinals want to fill from within, they could try first round pick Haason Reddick at inside linebacker, though he might be better suited on the outside on passing downs.