The 6-foot-2, 200-pound Harrison, of Lee's Summit (Missouri) West High School, was largely considered the top athlete in the draft, though he slid from the No. 17 spot on ESPN MLB Insider Keith Law's Big Board.
Harrison signed a letter of intent with the Huskers in February to play football for coach Bo Pelini and baseball for coach Darin Erstad.
Erstad, a former No. 1 overall pick in the baseball draft and longtime big-leaguer who played football and baseball at Nebraska, factored heavily in Harrison's college decision. The deadline for draft picks to sign with major-league clubs is July 15.
Harrison has been considered likely to bypass college for professional baseball if selected early in the draft. Pelini said after Harrison's college signing that the recruit had "every intention" of attending Nebraska.
Harrison caught 60 passes as a senior last fall for 1,007 yards and 13 touchdowns. He was rated as the No. 5 football prospect in Missouri and starred in basketball in addition to baseball.
This position for Nebraska is familiar. It lost quarterback signee Bubba Starling in 2011 in the final hour before the deadline after the outfielder, from Gardner, Kansas, was drafted with the fifth pick of the first round by the Kansas City Royals.
If the Huskers again fall short, the blow was softened somewhat by the transfer of Washington receiver Damore'ea Stringfellow. Stringfellow, a top-100 recruit in 2013, plans to enroll at Nebraska this fall. He likely will be eligible to play in 2015.
Harrison committed to Nebraska in July 2013 over offers from Arkansas, Iowa, Kansas, Kansas State, Michigan State and Missouri.