Tyler O'Neill declined to disclose why he missed time, and he explained that it was for a personal reason. He also said that his family had decided to keep it private, as is his right. The team was the one that assigned the "groin" label to the injury. At which point there is a question on what is newsworthy? Is it that he's going to miss time and how long he's going to miss time -- or is it a detailed examination of the precise injury a player had, who asked to keep the matter private? The answer in the scenario you present is actually the respect the player's privacy as long is does not give of the impression that he will be back sooner than he actually will be or that he covering up for the severity of the injury in a pennant race or when tickets are sold. That's the discussion that happens more often than you probably know, and there is definitely room for debate on the topic.
Which brings me to the biggest most important part.
This is essential: I will add, too, that to write about an injury that a player has withheld from the public, from the media, you better have rock-solid sources on what that injury is or else the report is wrong, and that's trouble. I have had times when I have sources confirming an injury that the player refutes. Absolutely denies. I better be right. I better be accurate.