The Hoops need to beat the Russians in the final game of Group G on December 5 and hope Barcelona do them a favour in the Nou Camp against Benfica.
Gary Hooper returned to the fray on Tuesday night as Celtic stumbled at Benfica, but McAvennie reckons Watt could be the key to unlocking Spartak – and landing a £3million Euro jackpot.
The former striker said: "I'd have no fear at all about throwing Watt into such a big game. He might not have a lot of experience at this level but he does have pace, power and an eye for goal.
"I won't burden him by comparing him to anyone, but to me he's a throwback to an old-school striker. He likes to take people on, he isn't afraid of putting himself about a bit and has a natural instinct for goal.
"He looks confident, he looks hungry and I fancy Tony will have a significant part to play in the Celtic team.
"I definitely think he has got something about him and we all saw that with his finish against Barcelona.
"Celtic will be going all out to win and, with Scott Brown and Victor Wanyama both out, it could be that Georgios Samaras drops into a wide left position and both Hooper and Watt start."
Hooper has been out with a hamstring injury and looks as though he needs some game time to get up to speed for the clash against Spartak.
The striker missed his chance of an England call-up due to the injury and will be desperate to regain his goal form on the biggest stage of all.
Hooper really caught the eye in the first match against Spartak and McAvennie believes the player will have rediscovered his edge in time for the return.
"I actually thought he did not too badly against Benfica, but that was always going to be a difficult shift, especially when he was just coming back into the team.
"A few of the lads look as though they are out on their feet because Celtic have played a fair bit already this season. I'd imagine Neil will rest one or two over the next few weeks, but Hooper won't be one of them.
"He'll want him to get as much game time as possible and hopefully get a couple of goals so he is going into this Champions League game with his tail up."