Can you post a pic? That will help us determine his age as well as get a better idea of his general condition.
He's probably dehydrated, so it's good to hear that he's drinking (and peeing!) I cannot stress enough how important it is to be very very careful so that he doesn't accidentally inhale water and develop aspiration pneumonia- it happens easier than you'd think. If you hold him up to your ear do you hear anything (like a clicking sound)? What does his breathing sound like?
Can you get a syringe? Thinking ahead to tomorrow, formula is going to be the next step after he's hydrated, and you'll need the syringe to feed him. This formula is great for older baby squirrels (which it sounds like yours is):
https://www.amazon.com/Fox-Valley-DAY-Formula-Squirrels/dp/B00EFX23LM
You can also make a temporary formula with goats milk & heavy cream. Do not give cows milk or any kind of human infant formula. The recipe is on page 3 of this link (the 'next page' button is easy to miss, located on the upper right). I suggest reading all 6 pages for a basic overview of what you need to know about caring for this little guy:
https://www.henryspets.com/1-baby-squirrel-care-guide/
Hopefully someone will chime in here who is more familiar with the Eastern Grey situation in the UK.
Thanks for helping this little one- they are so precious!
What I've done (with good success) for ones like this is to make them formula balls. They just can't grow up without the nutrition that they get either from their mom or from formula. Calcium powder won't be enough.
First you need a quality formula powder such as Royal Canin for puppies (best) or Esbilac for puppies. There is also a small company that makes a milk replacer especially for wildlife. You can get their baby squirrel formula either direct from the guy that makes it https://store.foxvalleynutrition.com/day-one-2050 or for a bit more on amazon here https://www.amazon.com/Fox-Valley-DAY-Formula-Squirrels/dp/B00EFX23LM
So I take
3 parts formula powder
1 part whole ground nuts like walnuts, almond or hazelnuts
1 part virgin coconut oil
and a little bit of fish oil, flax oil, hemp oil or any other oil that is rich in EFAs
I mix it with a fork, but you could also pulse it in a food processor. You want to get it to the consistency of pastry, which is to say looking like corn meal - still dry and flaky. It should not look like dough.
You take out little teaspoon sized lumps and roll them into balls in your fingers. As your fingers heat the coconut oil they will become more dough-like. Put the little balls on a plate and stick them in the freezer. When they are hard, take them out and put them in an air tight container in the fridge. Serve them cold.
They taste like marzipan, and I never met a squirrel that didn't like them. Once that orphan feels what all that protein and calcium is doing to her body, she will be hooked and want more. Hopefully she comes often enough for you to give her these regularly.
They're very filling, but try and make sure she gets 3 or more balls a day. If she buries them they will get mushy. so don't overfeed because it's a waste. Try to give her only as much as she will eat in front of you.
Basically her bones and muscles are so weak that she can't stand, I think. That's awful. But I have seen them make a complete and total reversal and even outpace their cohorts in terms of growth on these formula balls. They are an absolutely acceptable replacement for nursing.
You need to do it ASAP because her molars are coming in and will be very weak without getting a lot of calcium. I once knew an adult "wild" with broken molars who would sit in my lap to be petted while she ate. I believe that she was orphaned, like this one, at six or seven weeks and then grew up on soft foods and handouts from humans (such as bread) because she had no molars to chew seeds, cambium and nuts with. I think her molars came in too weak and broke off. Their molars don't grow constantly like their incisors do.
All this is to say that this one needs help or else she will have life long problems, if she can survive at all, that is, and survival is itself unlikely. Try to get some formula for her. I think you will be amazed at the difference it can make. I was.
Thanks for the info. You need to get this guy on a good diet right away.
First: He needs calcium, as the other poster said, he may be developing MBD which is fatal. Follow the guidance below:
https://thesquirrelboard.com/forums/showthread.php?32122-MBD-Treatment
Second: Absolutely stop feeding human infant formula. Goats milk alone doesn't have enough nutrients. Order "Fox Valley 20/50" formula online and start him on that asap (links below)
https://www.henryspets.com/fox-valle...formula-20-50/
https://www.amazon.com/Fox-Valley-DA.../dp/B00EFX23LM
While you're waiting for the fox valley to arrive here's a homemade formula recipe you can make:
3 parts goat's milk + 3 parts plain full fat yogurt + 2 parts heavy cream+ 1 egg yolk per cup of formula
Do not use commercial goats milk formula sold at feed stores. You ideally want fresh goat's milk from the grocery store or evaporated/powdered if you can't find fresh.
Fox Valley 20/50:
https://www.henryspets.com/fox-valley-day-one-formula-20-50-for-baby-squirrels/
General feeding info: