Mattison announced on his Twitter account that he will forego his final year of eligibility with the Broncos and plans to enter the 2019 NFL Draft.
"I can't tell you how much the last three years at Boise State have meant to me, being able to grow both as a person and as a football player," wrote Mattison on Friday. Coach Harsin, Coach Marks and all of the Boise State staff have prepared me for this transition and I can't thank them enough."
It marked the sixth straight year in which a player from Boise State has decided to leave the program early for the draft. The list includes a pair of second-round selections in Demarcus Lawrence (2014) and Kamalei Correa (2016), two fifth-round picks in running backs Jay Ajayi (2015) and Jeremy McNichols, and a first-rounder last year in Leighton Vander Esch.
Mattison had a superb junior season in leading the Broncos to their 16th consecutive bowl appearance, but their matchup against Boston College in Wednesday's First Responder Bowl was canceled 10 minutes into the game due to severe weather in Dallas.
The 5-foot-11, 210-pound Mattison rushed for 1,415 yards and 17 touchdowns in 13 games for Boise State (10-3), which won its final seven regular-season games. He also had 27 receptions for 173 yards.
Mattison closed the season in spectacular fashion with consecutive 200-yard rushing games, and rushed for at least 144 yards in his final four contests while amassing seven touchdowns in that span.
As a sophomore, Mattison rushed for 1,074 yards and 12 scores, averaging 5.1 yards per carry. He added 28 catches for 284 yards and a touchdown.
"I would like to thank my family for supporting my decision to attend Boise State University, which ultimately became one of the best decisions of my life," said Mattison. "Their love and support has helped me in the toughest of times and without them I would not be in the position that I am in today."