It's hard to see from that picture. Check to make sure there isn't a thread or hair something wrapped around toes, wrist leg etc... that is cutting off circulation. Have someone hold a good bright light, and even use magnifying glasses or reading glasses if you can, it's hard to spot hair and thread cause their fur hides it sometimes.
If there is hair or thread remove it carefully with something safe that won't nick the glider like a sewing seem ripper. Then slowly/gently message the limb and foot to get the blood flowing back.. Do NOT message it if you don't see anything cutting off circulation in case something is broken.
Watch it closely, take pics of it often, watch for color changes. If the tips of the toes or pad of the foot start turning black it's turning necrotic ( dead tissue)
If nothing is wrapped , look at your cage check for any rough spots, rust, broken bars, rough edges on toys etc, to see what else may have caused an injury.
Check to see if there is broken skin or a scratch or anything that may have gotten infected.
If you don't see anything visibly, ask the vet for an xray, perhaps he got snagged and twisted to free himself or something. What ever material the glider is in in that pic isn't glider safe material they get snagged on that stuff easily.