Lacy's one-year contract with the Seahawks includes a $385,000 bonus that is tied to his weight, a league source told ESPN.
It is unclear what weight Lacy needs to maintain in order to earn the bonus, but Seahawks coach Pete Carroll said Tuesday that he'd like to see the former Green Bay Packers running back play in the 240s.
"I want him big. I want him big and tough and strong," Carroll said on The John Clayton Show on 710 ESPN Seattle. "But I want him in the best shape so that he can run at his best and be durable and handle the load -- 235, that's at the time he came out [of the draft], he was there.
"But he's developed. Into his [240s], he's really dangerous."
The Milwaukee Journal Sentinel reported Tuesday that Lacy weighed in at 267 pounds during one of his recent free-agent visits. Carroll indicated that Lacy has been somewhat limited in what he can do because he is still rehabbing from a season-ending ankle injury he suffered in Week 6.
Lacy's deal with the Seahawks is worth up to $5.55 million, a source told ESPN's Adam Schefter. The contract includes $2.865 million fully guaranteed, plus an additional $2.685 million in bonuses tied to how often Lacy is active on game days, his weight and his total rushing yards.
A second-round draft pick in 2013, Lacy posted back-to-back 1,100-yard seasons to start his pro career and was the NFL's Offensive Rookie of the Year in 2013.
But his weight became an issue in 2015, when Green Bay coach Mike McCarthy said Lacy needed to come back in better shape after rushing for just 758 yards. After trimming down last offseason, he appeared to regain at least some of the weight he lost while working out with P90X founder Tony Horton, though he was still effective.