The former Hoops hitman spoke exclusively to Football Insider after Georgios Giakoumakis was dropped on Wednesday (9 February).
Giakoumakis, 27, has enjoyed a spell in the first team in recent weeks thanks to Kyogo Furuhashi’s injury and Daizen Maeda’s unavailability.
However, Maeda returned to the starting XI for Wednesday’s clash against Aberdeen but made way for Giakouamkis after 75 minutes.
McAvennie had previously told this site Giakoumakis could leave the club on loan in January due to the number of strikers on the books at Celtic.
He has now doubled down on the claim that the Greece international can play a vital role during the second half of the season.
“I said this last week, Giakoumakis has a big role to play,” McAvennie told Football Insider correspondent Ben Wild.
“When you play as many games as we will this season, you have to have plenty of options.
“I’ve been encouraged by Giakoumakis over the last few weeks. He has shown he has that physicality.
“The goals haven’t quite come for him but he has been quite unlucky.
“Kyogo is the main man and Maeda has hit the ground running. But if Maeda goes off the boil then who do we have?
“That’s why Giakoumakis is important. If he starts scoring goals then he will be pushing for that starting place.
“I have wanted this for ages. Competition can only be a good thing.”
Giakoumakis has scored three goals in 15 total appearances for Celtic this season.
He has appeared in the Hoops’ last six league games, starting four of them.