Manchester United boss Sir Alex Ferguson has shifted his focus to left-back as he looks to bring in cover for Patrice Evra during the current transfer window.Ferguson is short of defensive options on the left flank after sending Brazilian youngster Fabio out on a season-long loan to Premier League rivals Queens Park Rangers last month.The Red Devils are currently preparing for the first game of their pre-season tour of South Africa against AmaZulu on Wednesday night, and the veteran Scottish tactician admits he will test reserve-team duo Robbie Brady and Tyler Blackett in the left-back position, with Evra given extra time off following his involvement at Euro 2012 with France.Fergie confirmed last week he was still trying to make one addition to his squad ahead of the new campaign and it could well be an experienced left-back, with Leighton Baines of Everton touted as a potential target for the United manager."Left back is an area we're paying attention to," he said. "Because Evra is never injured, the opportunities haven't been there for Fabio. He is at QPR, we're just a little short in that department."That's why we're trying Robbie Brady, and we also have Tyler Blackett."Ferguson is expected to start with Brady against Usuthu in Durban, while Blackett should make his debut at some point in the friendly or against Ajax Cape Town on Saturday.