Sanders' absence was initially said by the team to be because of an illness, but then "personal reasons" were cited.
The former first-round pick out of Virginia Commonwealth signed a four-year contract extension worth $44 million last year after posting career highs in points (9.8), rebounds (9.5) and blocks (2.8) in 2012-13.
This season, Sanders' averages had dropped to 7.3 points, 6.1 rebounds and 1.4 blocks.
Reports surfaced this month the Sanders had told some Milwaukee officials that he was tired of playing basketball, a rumor his agent Happy Walters said was "unsubstantiated."
He rejoined the Bucks on Jan. 6 during a game against the
Sanders missed 25 games during the 2013-14 season after suffering an injury to his thumb during an incident at a nightclub.
He was also suspended for five games later in the season after testing positive for marijuana.
"It's a banned substance in my league," Sanders told the Milwaukee Journal Sentinel at the time. "But I believe in marijuana and the medical side of it. I know what it is if I'm going to use it."