The English striker joined Rangers in a £1.5 million move from Preston North End this past summer but he has struggled to justify that transfer fee so far.
The 28-year-old has netted eight times in 11 Scottish Premiership appearances but more is needed if the Gers are to enjoy a successful return to the top flight this term.
He has come in for some criticism this week from ex-Rangers man Neil McCann, but his team-mate Wallace tells the club's YouTube channel that the marksman is working very hard to prove himself a success at Ibrox.
"He's working ever so hard. He's always asking questions. He's good with analysis and always has good things to say. It's going to take time.
"Joe knows that he's going to be judged on goals - that goes without saying when you're a striker with Rangers - and I've got no doubt, with the work he's putting in, that he'll be rewarded."
Garner seems to have displaced Martyn Waghorn as Mark Warburton's first-choice number nine, but he will need to justify his inclusion - especially after what happened at the weekend.
Rangers, who visit Hearts tonight, came from a goal down to beat Partick Thistle on Saturday, with Joe Dodoo - another summer signing - coming off the bench to score twice and put Garner under serious pressure in the process.
Joe Garner (L) scores the first goal for Preston North End