The Denver Nuggets have become less optimistic about whether coach George Karl will return before the playoffs, NBA sources told Yahoo! Sports.

Karl recently needed treatment for blood clots in his legs and lungs that surfaced while he was already undergoing chemotherapy and radiation treatment for throat cancer, the sources said. The blood clots were treated successfully and Karl is expected to complete his cancer treatment at the end of next week, but the Nuggets aren’t confident he’ll feel strong enough to resume coaching at the start of April as was initially hoped.

Karl, who continues to have trouble speaking, will miss his eighth game on Tuesday with assistant coach Adrian Dantley also taking his place for the remainder of the Nuggets’ five-game trip. Sources said the Nuggets remain hopeful he’ll be back on the sideline for the start of the playoffs in three weeks, but they’re skeptical he’ll coach much before then.

“He’ll return – we just don’t really know the timing,” one source said. “It really depends on how he feels.”