The 6-foot-2 guard, who averaged 12.5 points per game last season, committed while on a weekend visit.
"I've known coach [Greg] McDermott and the coaching staff for a long time, and I trust them to prepare me for a great comeback," Foster said.
Foster had a huge freshman season (15.5 PPG) for Bruce Weber and the Wildcats but struggled on and off the court as a sophomore, including a three-game suspension in February for a violation of team rules.
Foster chose Kansas State over Creighton out of high school. He will sit out this season and have two years of eligibility remaining.