When deaaling with niggles....your fitness is unlikely to improve much AND is you're also unlikely to lose fitness. (Research confirms it takes around 3 weeks before yoyu start losing fitness)
With this in mind, when coming back you should pencil in a full rest day to prevent the cobwebs/scar tissue resurfacing.
What we do know - most injuries ARE recurrent injuries, not new ones. Indicating lack of conditioning to address the problem.... or too much too soon again. Good Luck!