Also, the team waived tight end Jake Ballard and confirmed that cornerback Brandon Hughes will be signed off the Giants practice squad by the Philadelphia Eagles.
If Ballard clears waivers, the Giants likely could bring him back to the practice squad.
Clayton signed with the United Football League on Oct. 25 after Tampa Bay cut him in September. But he was a first-round pick in 2004 and has a 1,000-yard receiving season under his belt -- although it did come in his rookie season. He worked out for the Giants on Tuesday.
The Giants' depth chart at wide receiver has no depth, however. Steve Smith could miss another two weeks with a pectoral muscle injury. Hakeem Nicks is out at least three weeks with swelling in his leg. Ramses Barden (ankle) and Victor Cruz (hamstring) were placed on season-ending injury reserve.
Clayton's best season was 2004 when he caught 80 passes for 1,193 yards and seven touchdowns. He never equaled half those stats in a season in the five years since.
The UFL has a transfer fee of $150,000, but a team source told ESPN.com NFC East blogger Matt Mosley that the Giants would not have to pay the fee.
Information from ESPNNewYork.com Giants reporter Ohm Youngmisuk was used in this report.