The forward netted a brace in Celtic’s 4-0 win over Ton at Lennoxtown on Wednesday but had been targeted by Ton boss Allan Moore prior to his scoring exploits.
The highly-rated youngster - who plays on the right wing - has made an impact at the Parkhead club, scoring in the 2-0 victory over Rangers in last season’s Youth Cup final.
The player, who is from Inverkip, has been on Ton’s radar for months and his arrival could not be more timely.
Moore is so short of personnel due to injuries that he will struggle to fill the bench against Cowdenbeath tomorrow, meaning Fitzharris could be thrown in to make his first senior start.
Although the player’s emergency loan period only lasts for 93 days, Ton could extend it, given that the player is under 21.
Moore said: “He is a right winger and scored two against us in a bounce match on Wednesday, which is hopefully a sign of things to come.
“He is only a young lad so we can’t expect miracles from him but he gives us a bit of balance on that right-hand side.
“The right side has been a problem this season and I think it is part of the reason why we haven’t scored a lot of goals. Sean is a direct player so we’re hoping he will make a difference in that regard.
“We are bringing him in to play in the first team, not as a squad player. He’s in there to fight for his place.”
The youngster first came to Moore’s attention at the Youth Cup final last season, which Celtic won 2-0 over Rangers.
He said: “I noticed him that night. He scored a goal where he came in off the left and fired a shot into the top corner.
“He can’t play at under-19 level any more, so that gave us an opportunity to get him.
“I am hoping we can hold on to him for longer than the emergency loan period.
“He is from Inverkip and hopefully his mum and dad will come down to watch him in the games.”