the side-stripes are hidden by the position and I'm not sure why the underside looks whitish, but this should be a plantain squirrel Callosciurus notatus (there are only two species left on Singapore, this one and the slender squirrel Sundasciurus tenuis, assuming the giant squirrel is now extinct there).
EDIT: I know that makes it sound like "it doesn't look like a plantain squirrel but it still is one" but it doesn't look like a slender squirrel so it must be a plantain squirrel I think. You can see the orange of the underbelly on the inside of the legs.
