United's latest deal is for Arsenal striker Chido Obi-Martin.
Cox told manutd.com: "Our recruitment team have been working hard to identify and register some high potential talent from across the UK. Hubert Graczyk, formerly of Arsenal, has joined our group of goalkeepers in the Professional Development Phase while there have been three additions to the group of first-year scholars, all from different backgrounds, showing the strength of our recruitment team.
"We welcome Samuel Lusale, Chido Obi-Martin and James Overy to the club. All three young players will join up with our Professional Development Phase as they adjust to life in Manchester and become acquainted with their new team-mates. It can be a difficult process for some players, while others slot right in.
"Whatever the scenario, our staff will be on hand to care for these young boys and make sure their experience at the Academy is an overwhelmingly positive one that sets them up for life. Good to luck to Samuel, Chido and James, well done to our recruitment team and congratulations to the families and wider support networks involved in these boys' journeys. Signing for Manchester United should be a proud day for everyone involved.
"I’d also like to take a moment to praise our outstanding recruitment staff, led by Luke Federonko. Their roles can be lonely and require unsociable hours and they don’t often get the same praise as the coaches, but they deserve to."