Selig was asked about the Guillen penalty during a visit to the press box during the Royals' game against the Milwaukee Brewers on Saturday.
"I haven't made any decisions on that score yet," Selig said. "We are working to finish off all the Senator Mitchell recommendations, which will really tighten the program up."
Guillen, the Royals' right fielder, was dealt the 15-day suspension on Dec. 6 for violations of baseball's drug prevention program. He has the penalty under appeal.
George Mitchell, in making his report on steroids and other drug concerns, recommended that the players named not be penalized and be given a "fresh start."
Selig is reviewing the cases mentioned in the Mitchell Report on a case-by-case basis.
He's occupied with trips to China and Japan this month for Major League Baseball's games in those countries and was not certain if he'd make a decision before the end of Spring Training.
"I don't know. It'll depend on how everything falls into place and how my time [is taken]," he said.
Even though Guillen's suspension is under appeal, there's no date determined for a decision.
"That's all a matter of timing and Rob Manfred and Michael Weiner have to work all those things out so I don't want to comment. That does not come to me, but I want to be very clear I'm just reviewing everything on a case-by-case basis," Selig said.
Manfred is MLB's executive vice president of labor relations and Weiner is general counsel for the Players' Association.
Dick Kaegel is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.