The Motherwell full-back is one of two reinforcements, along with Aston Villa's Barry Bannan, after six players were forced to withdraw ahead of the World Cup qualifier in Zagreb.
If given the nod, this weekend's match will see the 31-year-old earn only his second cap nine years after making his international debut. Well boss McCall said: "Steven has been a terrific professional in his time and he's had another consistent, good season so he has merited it."
He added: "The pleasing thing is that he's fitted in really well. I'm delighted for him and his family. It's a little bit of payback for all the effort he's put into his career."
Hammell is one of a number of players with limited international experience in a group which has been hit with the loss of Scott Brown, James Forrest, Lee Wallace, Danny Fox, Gary Caldwell and Liam Bridcutt.
But McCall believes those selected on the night should approach the match without any fear and make the most of the opportunity.
He said: "Prior to coming here, I thought to myself what our mindset will be when we meet up.
"Is it a case of let's go and play some good football and give the young boys a go and it doesn't really matter what the score is as long as they get good experience? Obviously you want to win every game you go into but is it damage limitation?
"Or is it just go and be the best you can be and maybe not prove people wrong but surprise people? I'm sure the majority of people across the world and even in Scotland are looking upon this as a really difficult tie, which we know it is.
"But I think the mindset is just to go out and be the best you can be and grab the opportunity. If you're making your debut, grab your opportunity. If you've had a few caps, help the people who are coming in."