"Adam's played a fair amount of non-league football in England, which is pretty rough and tough, in that left-side midfield role.
"To play there, you've got to be able to attack on the left side, you've got to be able to create and you've got to be able to defend."
At 1.90m, 22-year-old Tratt brings height and pace to Wellington's back four, where he'll slot in at right back in place of Louis Fenton, called into the All Whites for their friendlies this weekend against Mexico and the United States.
And while Wellington will be without New Zealand striker Kosta Barbarouses and midfielder Michael McGlinchey, Merrick is keen to finally unleash new signing Gui Finkler.
The former Melbourne Victory playmaker has been allocated fewer defensive duties, and seems to be relishing the extra opportunities up front.
"Gui's enjoying himself because I've given him a little more freedom on attack - he doesn't have to defend as much," Merrick said.
"We've got Alex Rodriguez, Vince Lia and Roly Bonevacia doing that job for him, so he's free to get forward as much as possible and get into goal scoring positions.
"I think Gui is going to score goals from open play, as well as from free kicks and set pieces."
- AAP