It’s a valid question as there is a level of Fitness (fitness for purpose) for everything we do.
The two variables are the purpose and required fitness level.
Andy Murray is struggling to make the right decisions about rehab to get him back to a level of fitness that enables him to compete at the top level. That’s his purpose and the consequent level he needs to attain. What’s your level and what do you do to achieve it?

Do you do this or something similar? https://www.youtube.com/watch?v=F_9Bmag3ee0
No, nor do I although it might work for her at her Level.

Do you lift weights and/or sit at one of the many shiny muscle workout machines at the gym?
https://www.youtube.com/watch?v=wdew6wIkX0M
You might want that sort of muscle definition but these types of workout won’t help your tennis.

Do you consider the walk from the car enough!
Honestly… it’s what most recreational tennis players do with a very few doing a couple of static stretches, which may help but are really inadequate to prepare for playing or to avoid chronic conditions developing.

Being fit to play tennis has taken on a whole new resonance at the top of the game over the last six months, which Murray’s decision to pull out of the Australian Open, only serves to underline.

It’s achingly clear that you need a level of fitness to play this game, whatever your ability, to get the most out of it, achieve your goals and play on for as long as you want without play interrupting injury.

The question remains, what sustainable level of fitness do you need for your level of tennis (or desired level), which begs the question how do I measure my level and consequently how do I develop it.
(I mean Fitness for Function, not some arbitrary measure of muscle strength or cardio capacity.)

3D Maps; Three dimensional Movement Analysis and Performance System can answer these questions for you and is included in your schedule when you book blocks of 4 or more Tennis lessons with me.

If what’s happening at the top of the game at the moment convinces you of your need to know your level of fitness for purpose and how to improve it sustainably then you need to read on. There is no Silver bullet, it’s 3D Maps… Three Dimensional Movement Analysis and Performance System.

3D Maps allows me to assess your movement capability, both mobility, and stability, in both directions of all three planes of motion. These aren’t measurements against some arbitrary standard, they are a record of your range of motion at the start of a process of sustainable improvements you can make. The analysis enables me to address your performance areas like skill acquisition, movement patterns, and pain signals, in ways that will benefit you.
It is an integral part of my sustainability coaching that will enable you to play the best tennis you can and dramatically reduce the risk of the types of acute or chronic injury that keeps a lot of recreational tennis players off the court for long periods of time. Injuries like tennis elbow, tennis leg, rotator cuff and a variety of other impingements are mostly not normal, not necessarily the result of aging, not inevitable and more likely to be avoidable with tennis sustainability coaching with me.  https://www.tennissustainability.com/
Video progress records and remote trainer exercises also available, on request, when you book a block of 4 lessons.

You only have one body, (as Andy Murray now appreciates) work with it and it will work for you, for longer.