Bizarre day for Joe McKnight

CORTLAND, N.Y. -- One day after being cleared to practice following a head injury, New York Jets running back Joe McKnight struggled Monday as he walked to the field, dropping to one knee three different times in a span of 75 yards.

McKnight lasted only 45 minutes in practice, as he was carted off after crashing to the grass while trying to haul in a deep pass. He received oxygen from the medical staff and, in a bizarre twist, ripped the media on Twitter, presumably tweeting while in the locker room.

Coach Rex Ryan didn't provide any details regarding McKnight's condition, but he said the team wouldn't have allowed him back on the field if there were lingering effects from the head injury.

"If the trainers felt he was at risk, he would never be out there -- ever," Ryan said.

McKnight missed nine days with what the team described as a head injury. Ryan refused to classify it as a concussion, although the team acknowledged that McKnight participated in the NFL's concussion protocol before being cleared. On Sunday, he returned to practice on a limited basis, wearing the red jersey for non-contact.

In a bizarre interview Sunday, McKnight refused to discuss the injury, using the same phrase -- "I'm not going to get into that" -- seven times in a three-minute interview.

It has been an eventful training camp for the enigmatic McKnight, who started off by flunking the conditioning test. He blamed it on dehydration. He also suffered a migraine and was arrested July 30 in New Jersey -- a day off -- for having outstanding traffic summonses. McKnight, one of the league's top kickoff returners, could be in jeopardy of losing his roster spot.

"He has plenty of talent," Ryan said, "but there's a concern about his durability."

The latest episode started about 10 a.m. as he walked to the field. He dropped to one knee next to a trash can, as if to vomit. A member of the training staff gave him a water bottle and he squirted water on his head. After about two minutes, he joined his teammates on the field.

Then came his quick exit, which Ryan said came on a "non-contact" play.

What happened next was unusual, to say the least. McKnight fired back at a fan on Twitter, thinking it was a beat writer, according to the Jets.

In subsequent responses, McKnight tweeted, "Now I'm getting into that" -- a reference to his line from Sunday. At one point, he seemed to be challenging the "reporter," tweeting, "Are you outside."

A Jets spokesman confirmed that the tweets came from McKnight.

McKnight actually returned to the practice field to watch the end of the session. He was seen wearing sunglasses as he left the field, declining interview requests. He told someone he experienced a migraine; he's had a history of migraines.

The former USC standout, a fourth-round pick in 2010, has been a high-maintenance player from the day he arrived. As a rookie, he vomited in a minicamp practice. Ryan said recently that McKnight experiences "anxiety" when asked to perform conditioning tests.

In other injury news, rookie quarterback Geno Smith practiced for the second straight day on a mildly sprained ankle. Smith, competing with Mark Sanchez for the starting job, limped noticeably. Sanchez took most of the first-team reps as the coaches tweaked the quarterback rotation. Ryan still hasn't said who will start Saturday night against the Jacksonville Jaguars.

"We're going to let it play out and see how we are at the end of the week," Ryan said.

It was an eventful practice. Pro Bowl cornerback Antonio Cromartie hurt his left elbow while trying to jam a receiver at the line -- he crumpled to the ground in pain -- but he didn't miss any plays. Third-string quarterback Greg McElroy left practice after aggravating an ankle injury he sustained in the preseason opener.

Wide receiver Santonio Holmes, 10 months removed from a Lisfranc foot injury that required two surgeries, provided no timetable for his return. The chances of his returning for the season opener are remote.

"Right now, I can't run," he said. "I continue to take it day by day and I do the necessary things to get better."

There was some positive injury news: Running back Chris Ivory, who suffered a hamstring injury before camp, practiced fully for the first time. Ryan said he hopes Ivory can play against the Jaguars.

"He looked excellent," Ryan said. "That's a big, powerful man. Every Jets fan is looking forward to seeing that guy run."