Hennessey later argued on Twitter that he was actually trying to get the attention of the person taking the photograph “to get on with it and at the same time put my hand over my mouth to make the sound carry”.
He added: “It’s been brought to my attention that frozen in a moment by the camera this looks like I am making a completely inappropriate type of salute.
“I can assure everyone I would never ever do that and any resemblance to that kind of gesture is absolutely coincidental. Love and peace Wayne.”
Hennessey, 31, featured in Crystal Palace’s 1-0 win over League Two side Grimsby Town on Saturday.