The flustered French keeper, thought to be furious after being made the scapegoat for the 2-0 defeat in some sections of the Scottish media, was asked by Advocaat if it was a serious matter and replied: "Very serious."
Charbonnier refused to talk to reporters and Advocaat was reluctant to be drawn on Charbonnier's outburst, saying only: "Like everyone here he is upset at the way the team played."
The temperamental Charbonnier, a talented painter who trains and owns horses, went to one of France's leading art schools, Les Beaux Arts.
He joined Rangers from Auxerre for pounds 1.2m in the summer of 1998, although after 19 consecutive appearances he damaged ligaments in his left knee last November against Bayer Leverkusen in the Uefa Cup and was ruled out for the rest of the season. He returned in August when Stefan Klos was injured.
Advocaat refused to comment further on his keeper's grievances, preferring to underline his belief that his side have the ability to surprise some of the best teams in Europe, including Bayern Munich.
Defeat in Spain on Wednesday night means Rangers need to pick up a point at least against last season's beaten finalists next Tuesday at Ibrox if they are to have any hope at all of progressing from Group F. The German club opened their European campaign by defeating PSV Eindhoven 2-1.
Advocaat, back at Ibrox at lunchtime after snatching only a few hours sleep following the midnight flight from the Spanish port, said: "Every day there are stories about Rangers so the expectations are very high but we have to be realistic.
"We have made 17 changes to the squad and have been together just one year. There is no shame in losing in Valencia but it was disappointing the way it came about. We fell short of our high standards and found it difficult to keep the ball and retain possession.
"But we are still in the rebuilding process. I am still looking for new players but it won't happen immediately, probably next season. We are just happy to be in the Champions' League and we have to get used to playing top teams like Valencia. Let's be content to be involved at this level.
The striker Rod Wallace, who has missed the last two games with a hamstring injury, trained this morning and could come into contention for the game against Bayern Munich.