Basically Channing said Greg is damned if he plays, damned if he doesn't -- especially if he's out there at only 75% to 80% and not able to keep up with his teammates. He also mentioned that it would be a disservice to the team to have to try and play with a guy who is not at 100% and they'd rather get him back fully healthy and ready to close out the season than have him hobbled and limping through the stretch run.
He also implied that the way that some fans and local media are turning on Greg probably only contributes to his depressed confidence level and shows other players on the team that Portland's so-called "great fans" are fickle and maybe not so great after all (this might be Channing projecting his own experience with the fans this year as much as anything).
His main point was that if this was a finger, a shoulder or any other part of the body that wasn't related to his legs then Greg would almost certainly be out there, but messing around with injuries to the lower extremities is a big no-no in the NBA.
There's a ton more in the interview and I'm only relaying a few of the points that stuck out to me without re-listening to the it.