GREEN BAY, Wis. -- Jordy Nelson was ready to joke about Eddie Lacy's weight loss, but for some reason, the Green Bay Packers receiver stopped himself.

He didn't need to, because the fourth-year running back's conditioning was no joke: It appears Lacy has taken it quite seriously.

The Packers saw that firsthand Monday, when players returned to Green Bay for the start of the offseason program. When they last saw Lacy, he was being called out by coach Mike McCarthy, who said his running back "cannot play at the weight he was at [last] year."

"I was going to crack a joke, but I won't. He looked good," Nelson said Monday. "We're glad to have everyone back, get ready to work. That will be for him to answer. I didn't ask him how much he weighed or his percent body fat or how fast he ran."

According to one source, Lacy has lost between 15-18 pounds since the end of last season. McCarthy denied a report this offseason that the Packers told Lacy to lose 30 pounds.

Lacy spent most of the last three months working out under the guidance of P90X founder Tony Horton, first in Wyoming and then in California before making his way back to Green Bay. He was not among the players available to reporters at Lambeau Field on Monday.

Several photos showing a much trimmer Lacy have circulated on social media during the offseason -- the latest of which came last weekend from an event at his alma mater, Alabama.

I have the best job in the world. #RollTide pic.twitter.com/zDgwzTNpW3 — Hannah Stephens † (@UASignGirl) April 17, 2016

"He looked good," quarterback Aaron Rodgers said. "Obviously been doing a lot of P90X."

The Packers listed Lacy at 234 pounds last year, when he struggled to his worst season as a pro with just 758 yards rushing in 15 regular-season games after posting consecutive 1,100-yard seasons in 2013 and 2014.

"I think Eddie looks good, man," Packers defensive end Mike Daniels said. "We'll see when the pads come on and everything, but I do think he's a guy who rises to the occasion. He comes from a great program where they do things the right way. He came under a lot of fire, so I think he's a guy that he got put on the spot and he responded."