The longer I thought about it, the less likely it is to ever happen.
Your creature definitely needs to have a strong and heavy tail to balance the body and use like a limb while standing up, since they have no arms.
The problen is the pelvic bone. Every land dwelling creature on earth has a more or less circular bone structure in the pelvis with the hip joints attached somewhere at the sides. The femural part of the hip joint always points sideways, even in humans. Having only one femur attached to the center of the pelvis is probably not stable enough to be able to hop.
And where do the intestines go? In every creature on earth the intestine and birth channel have to pass right through the pelvis. Your hopping alien would need a circular pelvic bone with a hole big enough to pass a fetus through it, while being strong enough to absorb the forces of hopping and landing without damaging the bone or soft organs.
The biggest no-go is evolution, though. You would have to gradually move both legs ever closer together until they start fusing at the hip. Now keep in mind that the hip joint is a ball-and-socket-joint to enable the movement of the legs in (almost) every direction. No matter how the femural part of the hip joint is designed at this point in evolution, fusing two ball-joints together yields one hinge joint. Your creature would most likely be unable to lay down, stand back up or steer its hopping because it couldn't move its leg to the sides.
Sorry, but not gonna happen.