"If there were a game right now, I would play," Harris told ESPN.com after limited participation in practice. "I'm probably about 75 percent."
"In another week, I'll be full-go."
Harris suffered the ankle injury when he came down awkwardly on his right foot while attempting to block a shot on Aug. 30.
"I was lucky," he said. "I thought it was worse than it wound up being."
The 6-foot-4, 210-pound shooting guard averaged 12.9 points per game last season and shot 41 percent from 3-point range despite dealing with an injured right shoulder for most of the season. He strongly considered leaving early for the NBA.
"My dream is to play in the NBA, and I was close to going," Harris said. "But I took everything into account. Am I trying to just go to the NBA or have a career in the NBA? I just felt it was the best decision to come back to school, improve and try and win a national title."
Michigan State returns four starters -- Harris, Keith Appling, Adreian Payne and Branden Dawson -- from a team that won 27 games a year ago. The Spartans are likely to open the preseason poll somewhere in the top five.