TNT sideline reporter Craig Sager was scheduled to work March Madness before canceling at his doctor's request. Now we know why. Sager's son Craig Sager Jr. announced that his father's leukemia is back on Sunday evening via Twitter.

Here's the statement from the family:

We wanted to ensure he was taken care of & that we knew what the next steps were before we shared this #SagerStrong pic.twitter.com/IhUM2nK8yl — Craig Sager II (@CraigSagerJr) March 29, 2015

Sager returned to television on March 5 for the Bulls-Thunder game after a yearlong battle with leukemia. He received an outpouring of support from around the basketball community for beating the disease.

Sager is most commonly seen as a sideline reporter for TNT's Thursday night NBA games, but he's been a staple in recent years at the NCAA Tournament, as well. The Illinois native has been working in broadcasting since 1972 and has covered everything from the Winter Olympics to World Series.