XML : Parse number in XSL with a thousands seperator

I'm trying to parse a number from an input XML file. The problem I have is that this number contains a grouping seperator. For example:

10,250.75

When I try to parse this using the number function I get NaN as the result. Is there any way to pass a format to the number function? I've found a lot of information regarding outputting a number in a different format, but not much for reading formatted input.

Example showing the problem:

  <xsl:value-of select="number('10,250.75')" />    

Gives the rseult:

  NaN    

Note - I am using XSLT version 1.