Ikegwuonu, who turned 22 on Monday, filed the appropriate paperwork with the league office to enter the draft, according to the Web site.
A two-time first-team All-Big Ten Conference selection from Madison Memorial, Ikegwuonu was supposed to meet with UW coach Bret Bielema last Friday to talk about the decision after the team returned from Tampa and the Outback Bowl.
Ikegwuonu started all 13 games in 2007, and led the team with 16 passes defended; a number that was second in Big Ten and tied for seventh-most in UW history. His 14 passes defended in Big Ten games led the conference and was part of the reason he was a consensus first-team All-Big Ten selection.
Ikegwuonu added 20 tackles and the game-clinching interception (his only pick of the year) against then-No.13 Michigan.
In 39 appearances, 29 as a starter, Ikegwuonu totaled 91 tackles, 5½ tackles for losses, six interceptions, 35 passes defensed, one forced fumble and one recovery.
Len Pasquarelli, who covers the NFL for ESPN.com, said Ikegwuonu is projected to be a "high-round selection," but scouts are anxious to see how fast he runs. Ikegwuonu has been timed at UW in 4.4 seconds for the 40-yard dash but the NFL does not have its own time on the junior.