Hixon tore his right ACL for the second consecutive year on Monday night against St. Louis, and will miss the rest of the season.
Clayton was with the Giants during training camp, but was one of the final cuts as the team trimmed its roster to 53. He did stand out on special teams in camp, blocking on kickoff returns in front of Devin Thomas. He was also a regular at Eli Manning's Hoboken workouts in the offseason.
"You never know what's going to happen, man," said Clayton, who was in Tampa with his family when he got the call from his agent. "But I'm thankful for the opportunity. I'm just glad to be back."
Giants coach Tom Coughlin had said cutting Clayton was an extremely difficult decision, calling the wideout a "consummate professional."
"It was tough, but it's part of the business," Clayton said of being cut. "Unfortunately in my case the numbers just didn't work out even though I was doing everything that I was suppose to. That's just the way it is."
Although he was out of a job, Clayton stayed active and had a feeling a call would come. Given that the Giants have already been snakebitten by injury, the opportunity arose rather quickly with the announcement that Hixon's season was over.
"I'm not sure," Clayton responded when asked what his role will be. "This is Day 1. It's the only work day I would have (this week). Obviously, I didn't get a lot of reps, so we'll play it by ear and see what happens. It's a day-to-day thing."
Asked if he'd be ready to play on Sunday in Philadelphia if activated, Clayton responded, "Absolutely."
"I'm gonna play my (butt) off every play and every opportunity that I get," he added. "That's all I can prepare for."
The 28-year-old Clayton spent his first six seasons with the Tampa Bay Buccaneers. The LSU product had a tremendous rookie season in which he had 80 catches for 1,193 yards and seven touchdowns. But he hasn't cracked 500 receiving yards in a season since and has just three TDs total in that span.
He played six games for the Giants last season, his first with the team, tallying two receptions for 19 yards.
The Giants might need Clayton to suit up Sunday, what with starter Mario Manningham also a question mark with a concussion.
"We just thought that it was better for us to have a little extra security at that spot in case we need it," Coughlin said.
Mike Mazzeo is a frequent contributor to ESPNNewYork.com.