Jeff Koons was sued for copyright infringement in the United States in 1992. He took the defense of fair use and subsequently lost it but won case on similar grounds in 2006. French law does not have a fair use defense as exhaustive as the United States and only certain articles provide for several uses of a protected work which the owner cannot oppose (for the purpose of caricature, parody or pastiche)
In the CJEU Deckmyn case, it was held that parody is an autonomous concept of European law and must be interpreted uniformly throughout the Union. Parody is an expression of humour and mockery and evokes an existing work (noticeably different from it).
The issue before Jeff Koons is to prove that the 1985 ad is still remembered and the sculpture is recognized as a parody of the Naf Naf ad. He may also contend that people were aware of the ad at the time of creation of the sculpture and current knowledge of the ad is irrelevant.