Broncos coach Josh McDaniels said Marshall's absence was simply a "precautionary measure" after he was sore following the team's first workout for rookies and rehabbers the day before.
Marshall had offseason hip surgery, but McDaniels wouldn't elaborate whether that's what bothered the Pro Bowl receiver.
"There's just a little residual soreness," he said.
The mercurial Marshall has made it clear he's unhappy in Denver. He skipped all the offseason workouts to protest his contract and for what he feels was a misdiagnosis of his hip injury by the team's medical staff.
Marshall posted a farewell to Denver fans on his blog last month. It came soon after his agent, Kennard McGuire, said team owner Pat Bowlen had informed Marshall in a private meeting that he would try to accommodate his trade request.
Yet Marshall remains with the Broncos.
The Broncos have already dealt one disgruntled player, trading quarterback Jay Cutler to Chicago after his rift with McDaniels.
But Marshall doesn't have the same kind of leverage. He faces health and legal issues, including an Aug. 13 trial in Atlanta on a misdemeanor battery charge. A conviction could lead to his second suspension from the NFL, which banned him from the opener last season following a series of domestic disputes.
In a news conference Monday, Marshall displayed his discontent through body language and quick quips on questions.
Then, he missed practice Tuesday.
But McDaniels insisted it was purely for health reasons.
"This was just a decision we made as an organization," McDaniels said. "When he's healthy and we feel comfortable with him, he'll be out there."
As for when that might be, McDaniels didn't know. The veterans report Thursday with the first practice in pads the next day, marking the official start of training camp.
Although Marshall may be dissatisfied now, fellow receiver Brandon Stokley thinks that when it's time to get down to business, Marshall will be the player who has turned in two straight 100-catch seasons.
"Once you see Brandon on the field, he's going to give 100 percent like he always has," said Stokley, who paid a social visit to Dove Valley on Tuesday. "We definitely need him out there to win games this year. He's going to be a big addition."
If Marshall were to hold out, he'd be subject to daily fines of $15,888.
McDaniels said it's just a matter of other first-round picks falling in line across the league.
"We're in constant communication and trying to work toward a resolution to get both players in here as fast as possible," McDaniels said. "I think that benefits them and it obviously benefits our team."