Sir Alex Ferguson believes Nemanja Vidic and Chris Smalling will be fit for the start of the season but is pessimistic about Jonny Evans' chances.
Rio Ferdinand is the only senior defender to have been included in the squad for Manchester United's current tour, but Ferguson is hopeful he will have two more centre-backs in time for the trip to Everton for their Premier League season opener on August 20.
"Vidic will start the season," the manager told reporters. "I am sure of that. He's still at that level of doing a good amount of training but not the competitive level that the other lads are at. He's better off staying at Carrington.
"Smalling has done a bit of training. He had a ruptured groin muscle which needed a lot of attention, but he's made gradual progress and we expect him to start the season."
Vidic has not played since rupturing cruciate ligaments in December, and Smalling had to undergo a groin operation towards the end of the season.
Ferguson was less positive about Evans, who has undergone surgery on the ankle he injured in April.
"Evans has had an operation," he said. "I'm not sure he'll start the season, but he won't be far away."
With Fabio having been allowed to join Queens Park Rangers on loan, Ferguson revealed he is set to test 20-year-old winger Robbie Brady out at left-back in the friendly against AmaZulu on Wednesday.
"Brady is an outside-left but we believe there's a possibility he will develop into a left-back," he said. "It's an area which we're paying attention to as Patrice Evra has played an average of 45 games in the last few seasons, so it's important for Fabio to get experience at QPR because, touch wood, Evra is never injured.
"The opportunities weren't there for Fabio and he needed more opportunities. With him away at QPR, we're a bit short at left-back so that's why we're trying Brady there. We also have Tyler Blackett with us. He's a strong boy, tall and quick, and he has time on his side. He is here for the experience."