Jeffery told ESPN's Joe Schad that he was "ready for the next step."
South Carolina cornerback Stephon Gilmore will follow suit and also make himself available for the draft, according to sources.
The thing to watch with both Jeffery and Gilmore is that neither player has retained an agent at this point. If they don't enter into an agreement with an agent or sign with an agent, they could still change their minds and withdraw their names from the draft. The deadline for underclassmen to declare is Jan. 15.
The 6-4, 229-pound Jeffery, who tied a South Carolina school record with 23 career touchdown catches, will almost certainly stay in the draft. He's rated No. 14 on Mel Kiper's latest Big Board of the top NFL prospects.
"I'm physical and can make plays in the red zone. I can make big plays in big games. I can work on my speed and get quicker," Jeffery told Schad. "I want to be like (NFL receivers) Larry Fitzgerald, Calvin Johnson and Andre Johnson."
Gilmore is not projected as a first-rounder and is more likely to change his mind and return for his senior season. He's been a starter since he was a true freshman and led the Gamecocks this season with 11 passes defended and four interceptions.