Les Bleus' head coach drafted his former Bordeaux protege into his provisional 26-man squad but left him out along with Montpellier defender Mapou Yanga-Mbiwa when he selected his final party of 23. Marseille forward Loic Remy had already been ruled out by injury.
The decision on Gourcuff was a particular surprise to observers craving his creativity but Blanc blamed the injury problems which restricted the 25-year-old to only 13 Ligue 1 appearances, and 10 starts, in the season just finished.
The coach declined to say whether a good performance in the friendly against Iceland, which France won 3-2 with two of their goals coming after Gourcuff's 75th-minute withdrawal, would have changed things.
But he told L'Equipe: "I have read that it is a gamble, but that is not what I do.
"We brought him with the intention that he would play a key role in the team. Unfortunately, after five days of training he suffered an ankle injury, a recurring injury.
"As he was already behind the others, there were too many risks."
Gourcuff's club-mate Anthony Reveillere was quick to dismiss any suggestion the midfielder cut an isolated figure in the squad.
"Not at all," he said. "Whether it is with the national team or at club level, we have to stop focusing on Yoann in this way.
"It's a shame for him, but I think it can be a positive for the future and I hope he takes it that way.
"Looking at how he finished the season, he was not missing much. Whether it is him or Mapou, they have a good future.
"I saw Mapou and wished him a good holiday. I will send Yoann my best wishes as well. Putting myself in the shoes of the two of them, it is obviously disappointing for them."
Yanga-Mbiwa missed out as Blanc opted to take only three central defenders - Laurent Koscielny, Adil Rami and Philippe Mexes - to the tournament.
His seven-strong defensive contingent instead includes four full-backs as 23-year-old Yanga-Mbiwa, who helped Montpellier to the Ligue 1 title and was summoned to join the squad after Tottenham's Younes Kaboul was ruled out, missed the cut.
"I thought about whether to double up at centre-back or full-back, and (Gael) Clichy showed excellent form and has a good attitude," said Blanc.
"I knew we would only play with two centre-backs. If there is a setback, the third can play. I made the choice and I will live with it."
He offered encouragement for the future to Heraultais youngster Yanga-Mbiwa, though, saying: "He is someone we discovered, someone who made a very good impression on us.
"In the future, he could be a contender for the national team. The man's mindset is exemplary. He is a great discovery for me and my staff."