SI.com first report the news that Niklas would not be back.
"I have made the very difficult decision to pursue my childhood dream and will enter the 2014 NFL Draft," Niklas said in a statement. "I have thoroughly enjoyed my Notre Dame experience and want to thank the University, Coach Kelly, my teammates, the football staff, administration, and my teachers, as well as all of my friends and the entire Notre Dame community for providing this Southern California native with the experience of a lifetime. While I will miss being part of the team next year, I will always be part of the Notre Dame family and look forward to returning to earn my degree from the greatest university in the country. Go Irish."
Niklas was third on the Fighting Irish this season in catches (32), receiving yards (498) and receiving touchdowns (five). He finishes his Notre Dame career with 37 grabs for 573 yards and six touchdown receptions, this after playing linebacker as a freshman.
Nicknamed "Hercules" because of his physique, the 6-foot-6, 270-pound Niklas entered Notre Dame as an ESPN three-star prospect out of Servite (Calif.) High in the class of 2011.
The move means all three underclassmen coach Brian Kelly submitted evaluation paperwork for ended up declaring for the NFL draft early, as Niklas joins defensive end Stephon Tuitt and running back George Atkinson III in passing up their senior years.
In his three previous years at Notre Dame, Kelly had just one underclassman declare early, current Minnesota Vikings tight end Kyle Rudolph.
Niklas' father had told ESPN.com shortly after the New Era Pinstripe Bowl that Troy had received a draft grade between the second and fourth round, and that the plan was to return for another year and graduate.
The news is of extra significance Thursday considering the Irish's top returning pass-catcher, DaVaris Daniels, told ESPN.com earlier in a statement that he was suspended from school for the spring semester for an academic matter. Daniels plans on returning to Notre Dame this summer.
Still, former starting quarterback Everett Golson will return from his own suspension this spring and now will be without his top-two targets for spring ball -- and, in at least Niklas' case, for the 2014 season.