Amavi made a slow start to the League Cup derby clash at Villa Park, but came out for the second-half with renewed vigour.
The 21-year-old burst down the line and delivered the cross which set-up Rudy Gestede to score the only goal of the game, to ensure Villa made it through to the next round.
It was a improvement which highlighted to Sherwood how much ability the French youth international has, but the 46-year-old boss says he needs to start believing in his own ability.
"I said to Jordan at half-time - show a bit more confidence," he said. "He's come to a big club. You're going to need a lot of bottle and in this game and he showed me he's got it.
"He can put himself about. He can get forward with real desire and belief. He did that in the second half. Jordan just needs reminding that he's a top player."
Amavi has been thrown straight into Villa's starting line-up since arriving from Nice over the summer, and he has shown the good and the bad in his game.
The energetic full-back has got forward with aplomb, but he has also made errors which stem from his inexperience.
It is hardly surprising that his confidence is so low, too, given that Villa have made a poor start to the season. The Claret and Blues have struggled to find form this term, but they will be hoping that the win over Birmingham can spark their campaign into life.