Picking up players that are currently on the Injured Reserve is a great way to secure the "rights" to a top-tier player without having to trade anybody for him or sacrifice any space on your roster until he gets back.
Here's now it works. First, find someone available on free agents or waivers that is listed on Injured Reserve. If you have at least one IR spot open on your roster, drop somebody to pick up that injured player. Immediately move him into your empty IR slot and then pick up another, active player to replace the guy you dropped (ideally someone at the same position). Viola! You just added someone to your roster pretty much for free.
Now just play the waiting game. Wait for whoever you added to get back from injury and your team will be stronger for it. Don't worry about using up your IR slot. After all, it's not helping you when it's empty. If someone already on your team ends up also getting hurt, you can decide which of the players to drop if and when it comes to that.
Here are five suggestions of top-tier players currently out with injury that you might want to target for this strategy: