The club said they were “appalled” by the behaviour of the individuals, who were filmed doing so at a recent friendly match with Sunderland.
Rigby, a soldier with the Royal Regiment of Fusiliers, was murdered by terrorists back in May 2013.
Celtic have insisted they will do their utmost to take “the strongest possible” action against those involved.
The statement read: “Clearly everyone at Celtic is appalled by these events. Such behaviour in no way represents Celtic Football Club or our supporters.
“We understand this incident is now subject to an ongoing police inquiry.
“Let us be clear, in the event that any individuals are identified as being responsible, Celtic will take the strongest possible action.”