The Hoops players know they need a win against Danny Lennon's team on Saturday in order to stay top of the table.
But despite having the prospect of playing against one of the best teams in Europe to look forward to Watt says his side will be not be distracted from their domestic duties.
"People say that all the time but you can only play what is put in front of you," the Scotland under-21 star said.
"St Mirren are the next team up for Celtic and if we don't beat them we will go into the Barcelona game on a downer so we need to win this match.
"I scored my first Under-21 goal at St Mirren Park and also netted a couple in the Youth Cup last season so it has been a good ground for me."
Watt has been in sensational form since bursting on to the scene last season with a double against Motherwell after coming on as a substitute.
Despite finding the net four times the teenager has started just three games for Celtic and says he doesn't consider himself an established first-team player.
"I am not a first-team regular as I have only started three games," Watt said.
"You cannot call yourself a first-team player after three appearances but if I play 30 games this season maybe I will look at things differently.
"I'd never get ahead of myself and I don't go out and tell everybody I am playing every week because I'm not.
"I am massively ahead of where I thought I would be at this stage of the season as I reckoned I would be in the reserves or out on loan.
"It is there in front of me and I know I am not a first-team regular although I don't see myself as back-up, more a member of the first-team squad."
Celtic will be without James Forrest and Scott Brown for the match against St Mirren after the pair picked up knocks while on international duty while fellow Scotland star Kris Commons is a doubt with a hamstring strain.
Meanwhile St Mirren skipper Jim Goodwin says the match against the Hoops will represent his side's toughest test so far this season but hopes the absence of Celtic captain Scott Brown will help the Buddies.
"We all know how important a player he is to Celtic," he said.
"He really is the heartbeat of Celtic's team. Hopefully with him missing that will play into our hands. But they have got such strength in depth."
Elsewhere on Saturday, second-place Hibernian face a tough trip to Dingwall to take on Ross County, second-bottom Dundee United will try and kick-start their campaign when they host Aberdeen at Tannadice and St Johnstone host Kilmarnock.
Hearts, who have been hit with a transfer embargo after failing to pay wages on time to some players and manager John McGlynn for the second month running, take on Motherwell at Tynecastle on Sunday.
Fixtures (1400 GMT unless otherwise stated)
Saturday
St Mirren v Celtic (1230), Dundee United v Aberdeen, Ross County v Hibernian, St Johnstone v Kilmarnock
Sunday
Hearts v Motherwell (1245)
Source: AFP
Source: AFP