PIE suffixes

From: gwalstawd
Message: 70684
Date: 2013-01-11

I'm working with a rather problematic Celtic river-name.

PIE *skw- would give sp- in P-Celtic.

Would it be reasonable to propose that a zero grade of *sekw- (1 or 2) could also give sp-?

Are there any PIE suffixes or extensions which could account for the vowels in a hypothetical *spue(:)?

I can't find anything in the standard works or by googling.

Thanks

Guto