Flux when speed of induction motor exceeds synchronous speed

When an induction motor rotor is made to run above the synchronous speed, it will inject electrical energy back to the supply. That is, the machine will start acting as a generator. In fact this method is sometimes used in regenerative braking.

When the rotor rotates at a speed greater than synchronous speed, the flux produced by the circulating current in the rotor will induce an opposing voltage in the rotor and make a reverse current flow back to the supply. At this time actually the torque and slip are negative. In this mode the mainflux will reduce, I think, as a reverse current is fed back.

Why do you think a reactive power will be injected back?