How likely to develop glaucoma after eye injury?

Depends on injury: If the eye suffered severe blunt trauma (enough to either cause bleeding inside or damage to the iris, lens or retina) there is a possibility.

Angle recession, etc: Blunt eye trauma can cause a recession of the irido-corneal angle, damaging the trabecular meshwork and diminishing the outflow facility. If the pressure is elevated, glaucomatous optic neuropathy may develop. Following recuperation from the trauma, all persons need baseline glaucoma testing, since the "sneak thief of sight" can manifest years after the original injury, painlessly. See an eyemd.

Very unlikely!: I depends on the damage from the trauma, and possibly the use of steroids to treat the trauma.

Increases over time: The link between blunt trauma recession of the anterior chamber angle and secondary glaucoma was established by wolff and zimmerman in 1962. The risk is 3-4% in the first year and 10% later on. Other eye trauma features associated with increased risk are hyphema (blood in the anterior chamber), excess pigment clogging the trabecular meshwork, elevated baseline eye pressure, and lens displacement.