But there was a more plausible reason to come.
The fourth-round pick needed wet towels and breaks in the morning, and dropped at least four passes in one drill. After a more successful late-afternoon practice on the grass field, McKnight admitted his fitness level wasn't what it needed to be.
"I'm not in good shape right now," said McKnight, who at one moment was crouched under the uprights as trainers poured water over his head. "I'm in OK shape, but not the best. I could be better."
He said that he was going to see if it's possible to stay around Florham Park for a few extra days, to work out and prove to the coaches that he has the drive and stamina to be a productive running back when the season comes around.
"There's nothing to beat around that," McKnight said. "I've got to show them what I can do to get on the field."
Jets coach Rex Ryan downplayed McKnight's struggles. He said plenty of other players have had bad showings in their debut as a pro, such as running back Shonn Greene last year.
"He's fighting through it," Ryan said of McKnight. "It's funny, every time I look around he's got a wet towel around his neck and he's got [running backs coach] Anthony [Lynn] barking all over him, and then he's making one mistake after another -- and then you put the ball in his hand and he's pretty good.
"Sometimes it takes a player a little longer to play like a Jet."
McKnight was one of the lucky ones at the rookie camp. For many of the undrafted free agents and tryout players, it might be their last weekend of competitive organized football. McKnight said Lynn made him fully aware of what he was doing wrong.
"He didn't like the way I was throwing up and everything," McKnight said. "He was just telling me that professionals don't do that. Once you're here, there are a lot of people in the world dying to be in this position and I just got to take full advantage of it."
McKnight seemed a bit chagrinned by the dozen or so reporters waiting to speak to him. He had been with trainers during the time the rookies were available to the media, so he was brought over after the second practice.
There was a lot that was more intense from his days at USC. The criticism, the scrutiny -- even the way practice itself was run. This was different, McKnight said, contrary to USC's reputation for tough practices.
"That's what they say. Coach [Pete] Carroll was a pro coach before he came to college," McKnight said. "[But] practices were not like this."
McKnight said he was concerned that he'd failed to show his skills, but the one man he needs to impress, Ryan, didn't seem too outwardly concerned by McKnight's physical issues.
"I don't think we need to overreact with this," Ryan said. "He still does some great things out there."