Welsh international Hartson has been thrust into forming a partnership with Bhoys hotshot Henrik Larsson following an ankle injury to Chris Sutton, but he limped out of the 4-0 romp over Dundee United with a foot problem.
Hartson left the ground with a heavily strapped foot, but he reports no broken bones.
"I don't think anything is broken but I'll have to wait to see how it settles down," commented Hartson.
"I'm struggling to get a shoe on it at the moment and we'll have to see how it goes."
With Sutton sidelined for over a month, Hartson will have a key part to play and Bhoys boss Martin O`Neill will be desperate for him to figure against Motherwell on Wednesday.
Crainey, meanwhile, left the Tannadice pitch in agony following a tackle by Jim Hamilton, but X-rays have shown no broken bones, although he will have to wait for tests to ascertain whether there is ligament damage.
Hamilton, meanwhile, has apologised for the tackle on Crainey, but claimed there was no malice involved.
Speaking to the Daily Record, Hamilton said: "There was no malice in it - I am not that kind of player.
"I'm glad Stephen hasn't suffered a break or a fracture and isn't as seriously injured as we all first thought. It was just a mistimed tackle and I certainly didn't mean to injure him.
"I am glad it looks as if he is going to be all right because I feared the worst. But it wasn't deliberate on my part."
