Hackenberg still plans on playing for Penn State this spring, according to the team.
Penn State fell to 0-5 in conference play with a loss to Illinois.
Penn State will play 10 games, solely against Big Ten opposition, in the 2021 spring season.
"It is with excitement and gratitude that I announce my retirement from professional soccer."
Penn State's big man had a big afternoon against Purdue. Despite the loss, Harrar's impact should be important in the coming weeks.
A strong start to the second half was enough for Purdue to beat the Nittany Lions on Sunday afternoon.