Nathan Lyon has revealed recovering from his hip injury required extensive rehabilitation as he defended missing NSW's last Sheffield Shield match to attend the Australian Grand Prix. Australia's greatest-ever finger spinner had initially downplayed the injury he suffered during the triumphant home India series and that lingered on the tour of Sri Lanka. But on Monday, Lyon said bouncing back to fitness had amounted to a full-time job since returning from the clean sweep in Galle in mid-February. He has since recovered so is set to feature in the World Test Championship final in June and would likely have played the Shield decider had NSW qualified. But Lyon and fellow Australian teammate Usman Khawaja raised eyebrows attending the Formula 1 in Melbourne on the same weekend their respective sides played for spots in the Sheffield Shield final. "I'd been medically ruled out, to clear all that up," Lyon said at a media conference for the launch of next summer's international fixtures. "The plan was to play the Shield final if NSW were lucky enough to get in there but that wasn't the case. "I've been doing a fair amount of rehab, pretty well five days a week. That's the reason I didn't play the Shield game. "I love playing cricket for NSW and state cricket. Any opportunity, I'll play. But in saying that, the F1 was pretty good." Lyon had ripped tissue off the fascia in his left hip, and was in pain if he landed on it. The area also filled with fluid when Lyon ran so required draining more than once. "(It's) all well and good now," he said. On another issue, Lyon said it was "really hard" to comment on whether Matthew Kuhnemann should have been permitted to undergo testing on his bowling action behind closed doors. Kuhnemann was reported for a suspect action only days after finishing the two-match series against Sri Lanka as Australia's best bowler. Lyon was "pretty heartbroken" for his teammate, who was ultimately cleared in late February. "I'm not sure what the actual process was with the match referees and the officials. It would've been nice if it was kept under wraps and they could've gone through the process behind closed doors," Lyon said. "I was pretty heartbroken, in a sense, I actually flew home with him and he was pretty gutted when he was talking to me about what he had to do. He was pretty nervous. "For him to have his name cleared, I couldn't be prouder."