What it says in the rulebook is
i. In the case of a vacancy for leader or deputy leader, each nomination must be supported by 12.5 per cent of the Commons members of the PLP. Nominations not attaining this threshold shall be null and void.

ii. Where there is no vacancy, nominations may be sought by potential challengers each year prior to the annual session of party conference. In this case any nomination must be supported by 20 per cent of the Commons members of the PLP. Nominations not attaining this threshold shall be null and void.

To me that's pretty clear cut. There is no vacancy. And it's potential challengers that need to get 20 per cent of the PLP to support them. So the current leader doesn't need to do that.