Hartson believes the winger is still one of Celtic's top players but feels he is no longer hitting the heights of previous campaigns.
The former Celtic striker insists last season, in particular, saw McGeady fail to make as much of an impact and that he could find himself with the option to move on if the price is right.
Hartson said: "Aiden has dipped in his performances over the last couple of years. Earlier on in his Celtic career he was absolutely phenomenal.
"He had problems with Gordon Strachan and his performances have dipped for such a great player.
"Maybe the club will look at that and may look to cash in on him, but he is a very important player for the club.
"He is one of the top players there and I'm sure they will discuss it at board level and decide what to do with Aiden.
"He wasn't as influential last season for sure as he has been in previous seasons so they may look at that."
Asked whether the time is right for him to go, Hartson added: "I can't say that. He's a young boy and he will make his own decision along with his advisors. All I know is, when Aiden McGeady is playing well, Celtic are a better side for it."
McGeady has been linked with a lucrative move to Spartak Moscow – who recently had an 8.3million bid rejected – while Aston Villa and Birmingham are also reportedly interested.
But Hartson does not believe a switch to Russia is on the cards for the Republic of Ireland international.
"I would be surprised because I think there are better leagues to go to," he said. "If I was his agent, I wouldn't be looking for him to go to Russia, I would be looking for him to go to the Premiership or stay in Scotland or Spain or Italy.
"There are better places to play your football week in, week out than Moscow, but it's entirely up to him."
Meanwhile, Hartson believes Rangers are slight favourites to win the championship because Walter Smith's last season in charge could have a bigger impact on the title race than Neil Lennon's first at Celtic.
He said: "I think it will be tough this year, I think Celtic have it tough, because the Rangers players will just give that little bit more because it's Walter's last year.
"That's what I would expect them to do. They would love to give him a send off with his three titles in a row. I make them slight favourites."