The Bournemouth loanee arrived at Ibrox in January, poised to spearhead Rangers' title charge.
But Celtic have since pulled clear at the top once again, while Defoe has struggled for minutes on the pitch.
The 36-year-old has only started four games for the Glasgow outfit, mainly due to the form of striker partner Alfredo Morelos.
And Gerrard admits he understands why Defoe may be feeling frustrated following his move north of the border.
"Knowing him better than most, he's probably been a bit frustrated with me in terms of game-time and minutes," he told Rangers' official YouTube channel.
"I know him very well.
"But I spoke to Jermain, he's come in and done really well and I've got every confidence that he'll continue to build on last night's performance and he'll start again at Motherwell and we'll go from there."
Defoe started this week's clash 3-0 win over Hearts, netting in the process.
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And the veteran forward will likely get more chances in the coming weeks as Morelos sees out his suspension.
The Colombian earned his fifth red card of the season during last weekend's Old Firm derby.
But Gerrard has promised to help the hot-head going forward.
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"I had similar actions when I was younger," Gerrard said.
"You have to have a long look in the mirror and think about what your team-mates and supporters have to go through once he leaves the pitch. You have to think of other people.
"Now it is just a decision for the club to decide where the fine goes to, but Alfredo has accepted, shown remorse and apologised.
"I think he made that public himself, which is the right thing to do and we draw a line under it.
"Moving forward, we hope Alfredo learns the hard way and we wait now for him to return to help us in the final push."