Gourcuff, who had two mediocre seasons at Olympique Lyon, was included in a preliminary 26-man squad as the only proper playmaker but he failed to impress in a 3-2 friendly win over Iceland last Sunday, picking up a minor ankle injury in the process.
The squad was trimmed to 25 when striker Loic Remy was ruled out of Euro 2012 because of injury and Blanc on Tuesday had to drop two players before submitting his 23-man squad to UEFA.
Gourcuff and Montpellier centre-back Mapou Yanga-Mbiwa left the squad after lunch.
"We had picked him because we wanted him to have an important role in the team," Blanc told a news conference at France's training camp in the sea resort of Le Touquet.
"Unfortunately, after five days, after the game [against Iceland], after another ankle injury, there were too many uncertainties surrounding him."
Gourcuff, whose form nose-dived after leading Girondins Bordeaux to the French title in 2009, played only a few games for Lyon this season.
"He was behind [physically]. This injury is annoying but it's not just from the match, it's a recurrent injury," Blanc added. "There were to many uncertainties."
France, who are drawn in Group D with co-hosts Ukraine, England and Sweden, take on Serbia in a warm-up game in Reims on Thursday.
