"We are very disappointed by Laurent's actions, which are against our clear instructions. We hope to resolve this matter and will not be providing any further comment at this time," the club said in a statement.
Arsenal will play their opening match against Colorado Rapids in Denver on July 15 followed by a match against Bayern Munich in Los Angeles, Fiorentina in Charlotte and Real Madrid in Washington DC.
Arsenal 29-man squad
Leno, Martinez, Bellerin, Sokratis, Holding, Monreal, Mustafi, Chambers, Jenkinson, Mavropanos, Kolasinac, Mkhitaryan, Ozil, Maitland-Niles, Xhaka, Lacazette, Aubameyang, John-Jules, Nketiah, Saka, Smith Rowe, Nelson, Olayinka, Burton, Willock, Medley, Macey, Thompson and Martinelli.