Abrupt switching of phases

If a sprinter in training is not improving at the rate that he should, and it becomes clear that thete is a basic fitness and strength issu, for example he hasn’t been through a gpp, and just went straight into competing, how would this be handled?? Do you continue in the current trent and phase or do you cut short the phase and roll into a new GPP phase to get all the basics back in place??.

Anyone can read this and understand what I’m tryin to say, please give me a handa