While the Coyotes were open to adding another option to their defense in the waning weeks of the summer, the blue line appeared to be set. They acquired a partner for Oliver Ekman-Larsson on the top pairing in Niklas Hjalmarsson and beefed up their depth with the signing of Adam Clendening. But what the back end could look like when the Coyotes debut Oct. 5 is now up in the air since Jakob Chychrun is sidelined indefinitely after undergoing knee surgery Thursday to repair an injury suffered this week during offseason training. The Coyotes said Chychrun is expected to make a full recovery, and they will provide a further update once training camp begins Sept.14. They did not elaborate on the nature of the injury and declined to share any specifics about it or his recovery, so it’s unclear when, where and how the injury happened and what’s next for Chychrun – who became a social-media hit earlier this summer when he posted a video of an impressive box jump during his training. This setback comes on the heels of a strong rookie debut for Chychrun, who cracked the lineup as an 18-year-old just months after getting drafted 16th overall last summer. He posted seven goals and finished with 20 points in 68 games, flashing plenty of potential as a smart, offensive-minded defenseman who began to earn more ice time as his play in his own end improved.