It all changed Sept. 15, 2014, when Mantha, a first-round pick (No. 20) in the 2013 NHL Draft, sustained a fractured right tibia at the Traverse City Prospects Tournament. At the time of his injury, which sidelined him all of training camp in 2014, he was leading Red Wings prospects in goals, points and shots on goal.
Mantha missed two months before finally making his professional debut with the Grand Rapids Griffins in the American Hockey League on Nov. 14, 2014. He struggled upon his return, scoring 15 goals and 33 points in 62 games. The lack of offensive production didn't sit well with Red Wings senior vice president Jimmy Devellano, who expressed with the local media his disappointment in Mantha's performance.