The 19-year-old midfielder is a free agent having spent the last year working under former Light Blues defender David Weir in Everton’s reserves.
Prior to that, the Republic of Ireland youth international spent time working at Norwich City and he has also been involved in England’s age group teams.
Although Kelly didn’t make any first-team appearances at either Carrow Road or Goodison Park, he does come with good pedigree.
And McCoist has been encouraged by what he has seen from the teenager in his first couple of session working with the League One leaders.
The manager said: “Sam’s a player who was recommended to us by Ugo Ehiogu and also Steve Kutner, one of the agents from down south.
“Sam has good pedigree and you’d have to say looking at that, he’s certainly got to have something about him."
“He has come up and has looked great in training. He’s very, very quick, he’s comfortable on the ball and has a lovely left foot.
“Sam has already started moaning about the amount of running he’s having to do in training but I’ll take that as a backhanded compliment about what we’re doing here.
“He has fitted in with the lads well and he’s up here for a week so we’ll just monitor him and see how it goes.
“Sam has good pedigree and you’d have to say looking at that, he’s certainly got to have something about him.
“From seeing his training sessions, I can back that up. It’s very early days but he’s enjoying himself and we’re certainly enjoying having him.”
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