Rangers signed Defoe on an 18-month loan deal from AFC Bournemouth.
Defoe, 36, joined Rangers on their mid-season trip to Tenerife after agreeing an 18-month loan deal with Steven Gerrard's side from English Premier League outfit AFC Bournemouth.
The 57-time England international could make his debut on Friday night as the Gers travel to Cowdenbeath to face the minnows in the fourth round of the Scottish Cup. He is expected to sit ahead of Lafferty in the pecking order.
Indeed, Celtic legend McAvennie believes something is wrong with Northern Irish talisman Lafferty, and reckons Defoe has joined the wrong team in Rangers - over Celtic.
“Being a striker myself I notice certain things. He keeps himself very fit. He doesn’t drink or anything – I don’t know how he’s made it in football. Seriously, though, he has kept himself fit," McAvennie said.
"He is a good lad as well. He will score goals, that’s for sure. Listen, he scores goals wherever he goes. Shame he’s going to the wrong team. Rangers needed cover. I don’t know what’s wrong with Kyle Lafferty, but he’s not getting a game.
"They needed somebody to come in. They are creating chances. The fact [Alfredo] Morelos, who misses more than he scores, is the top goal scorer just shows you that. It is a concern [for Celtic]."
Defoe has been left on the sidelines at Bournemouth for much of the campaign, managing only 21 minutes of Premier League football spread across four substitute appearances this season.
But his signing has caused a stir in Scottish football, with the calibre and quality of Defoe giving the Teddy Bears plenty of optimism in the Scottish Premiership title race.
Lafferty, meanwhile, has been made to play second fiddle to top scorer Alfredo Morelos since rejoining the club from Hearts. With Defoe on board, it remains to be seen what kind of part Lafferty will play.