The Greek striker seems poised to quit the club and has been linked with a January move that would see the Hoops recoup a transfer fee for the out-of-contract star.
Lennon is in the market for more players as he bids to bolster his attacking arsenal before the end of the month.
And Hay admits he will have to think carefully about team selection if Samaras does opt to see out the remaining months of his deal before clinching a Bosman switch this summer.
He said: "I think it's a case of when, not if, he leaves.
"He could go in January or he might wait until after the World Cup.
"From Celtic's point of view, if he is not going to sign a new contract, they might think it is better for him to leave just now.
"But the decision is down to Georgios, not what Celtic decide.
"The ball is in his court and I have got a feeling that he might wait until after the World Cup before he moves on.
"I think Celtic would prefer it if someone came in and paid money for him because they will get nothing for him in the summer.
"I don't think it will be a case of him downing tools. He has got a place at the World Cup to play for.
"But, if he doesn't sign, does Neil Lennon continue to play him? It's a decision for Georgios as to when he goes but Neil is in the position of deciding if he plays him or not.
"Celtic will win the league with or without him so it will be interesting to see what Neil does with him if it becomes clear he isn't part of his plans for the long term. That will be down to the manager."
While Samaras is poised to bring the curtain down on his successful Celts career, midfielder Joe Ledley could extend his Parkhead stay.
The Welshman has been offered fresh terms by the champions and Hay is keen to see the deal signed and sealed as quickly as possible.
He said: "In these instances, it is not what you hear, it is what is done. Until the contract is signed, nothing is confirmed.
"There is still a chance that Joe could move on, but it seems to be that there are more positive noises coming from his camp.
"Like Samaras, he could still move on. Celtic have already signed Stefan Johansen from Stromsgodset so they have someone left-sided who can play Joe's position.
"If he does leave, Neil will feel that he is covered in that area of the park."