"Going in," he wrote.
The Mavs have been tight-lipped about Butler's condition since a source said the symptoms indicated that he suffered at least a partially torn patellar tendon in his right knee during Saturday's loss to Milwaukee.
A fully torn patellar tendon would be a season-ending injury. A partially torn patellar tendon would probably sideline Butler for a couple of months.
Butler followed up the photo with a couple of optimistic tweets.
Championship! Remember that fans that's what its about and we have what it take in that lockeroom to get it done, ill be 100 percent
In no time, and I will be the biggest supporter on the sideline until healthy thanks for the support again I'm going in....