Butler was vociferous and intense throughout scrimmage sessions, targeting president of basketball operations and coach Tom Thibodeau, general manager Scott Layden and teammates, including Karl-Anthony Towns and Andrew Wiggins, league sources said.
It's not clear what Butler's outburst means for Minnesota.
Minnesota's star swingman, who has been at odds with the organization for almost a month, requested a trade from the Timberwolves on September 19. Butler and his representatives have reportedly grown frustrated by how the Timberwolves have handled his trade request.
The T-Wolves' first game of the season is on Wednesday when they visit the San Antonio Spurs.
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The practice comes after sources said that the Heat were still pressing for a trade to acquire Butler. The Heat reportedly pushed the Timberwoles to "accept a revised offer" for Butler with a deal potentially centered around center Bam Adebayo, guard Josh Richardson and a first-round pick.
"Outside of the Heat, the Timberwolves have had no serious, active talks with any other team", ESPN reported in a separate story.
The Los Angeles Clippers and Houston Rockets also haven't given up on the idea of landing Butler in a trade, according to multiple sources and reports.
Butler, an upcoming free agent in 2019, returned to the Timberwolves for practice Wednesday even though he's continued pushing the franchise to trade him elsewhere.
While the Butler saga seems to be dragging on, it's only been three weeks, as one GM pointed out to AmicoHoops.