Shannon entered the NBA draft last spring before withdrawing and returning to school. Texas Tech said it is holding him out "out of an abundance of caution ... to ensure there are no possible issues resulting from that process and that all NCAA rules were followed."
Shannon won't play until the review is completed.
A 6-foot-6 junior from Chicago, Shannon averaged 12.9 points and 4.0 rebounds last season and was expected to be an anchor for new head coach Mark Adams. He was named preseason first-team All-Big 12 and is the team's leading returning scorer.
Shannon isn't the first former NBA draft entrant to have eligibility issues this month. Illinois star center Kofi Cockburn was suspended for the first three games of the regular season for selling "institutionally issued apparel and memorabilia" before he decided to withdraw from the draft and return to the Fighting Illini.
Texas Tech opens its season on Tuesday against North Florida, but won't play a power conference opponent until December when the Red Raiders travel to Providence and then face Tennessee at Madison Square Garden as part of the Jimmy V Classic.