The team used the second overall pick in the 2011 Draft to acquire the forward, who averaged 12 points per game last season.
The Timberwolves' head of basketball operations told KFAN 100.3: "I do believe that Derrick has an opportunity. He's lost weight. He wants to come in a lot lighter to be able to play some small forward, also play some power forward as a stretch four.
"Derrick hasn't lived up to that second pick in the draft. Now, part of it's his fault, you always have to take responsibility for yourself as a player.
"The biggest thing he has to do as an inside player, he misses a lot of easy shots. He plays small at the rim, and part of that is he doesn't locate the rim. It's almost like he shies away from some contact."
Williams scored a career-high 28 points against the New Orleans Hornets in March.