Manziel won the 2012 Heisman Trophy as a freshman quarterback, leading the Aggies to an 11-2 record, including handing eventual BCS champion Alabama its only loss of the season.
However, since the end of the season Manziel has been in a series of attention-grabbing situations. Most recently it was alleged he received money for signing autographs.
The NCAA and Texas A&M issued a statement Wednesday that there "is no evidence that quarterback Johnny Manziel received money in exchange for autographs, based on currently available information and statements by Manziel."
"Due to an inadvertent violation regarding the signing of certain autographs, Texas A&M declared Manziel ineligible and submitted ... conditions for reinstatement to the NCAA," the statement said.
The conditions are that Manziel sit out one half of a game -- A&M selected the first half of the No. 6-ranked Aggies' game Saturday against Rice; that the quarterback address the team about the situation and "lessons learned"; and Texas A&M is to revise its "future education regarding student-athlete autographs."
The NCAA said the investigation could be reopened if additional information was presented.
Manziel, 20, completed 29-of-434 passes for 3,706 yards and 26 touchdowns against nine interceptions last season.