Well I see it is healing up, could it have been a string trimmer. To assume this was caused by an animal I think you would see some teeth marks. If is healing all around I would do nothing but to insure it stayed dry, or at least that is the advise for my area. I would then fire the gardener or at least look at the trimer and every type of string or blades they use. How far from the ground is this damage, but that doesn't mean much if it was a string trimer, I have one and I use a plastic/wire embedded string and it would make a cut just like that one if I got sloppy. could this be plausible? Animals mostly only eat the bark of very young trees, dear some times scrape there horns on trees, however it would do more damage then this plus they also break branches.

String trimmer? I doubt that very much because such injury is typically at the soil line.

Whatever made the wound is long gone. And, as has been said, the tree is beginning to cover the wound.

Beyond that, the wound has been there a long time -- likely you just didn't notice it -- as shown by the sizeable rolls of wound coming in from the sides. This new growth will eventually cover the bare wood you see.

as long as the tree isn't completly girdled it will most likley be fine if disease hasn't gotten in there by now it won't....it has basically healed... who knows what caused it trimmer mower or whatever it was severly gashed ...DO NOT coat with anything let it continue to heal over ...I see no problem here unless the non showing back is girdled then all bets are off ...David

Very nice tree, glad I bought one.. mine is about a ft tall now so I know now what to expect in 5 yrs.. sorry dont know what is wrong with the maple, definitely looks like something is eating it..