When you embed your excel sheet in your word document, are you embedding it or linking it. You can read a little bit about the difference in this document by expanding the "An introduction to linked and embedded objects" section. The article mentions that when you embed objects are stored within the parent document, while linked objects are referenced by the parent object.
As Andy has mentioned, a linked object will not work because the second document isn't on the same file system, even if you also upload it to the same Confluence document.
It's possible that an embedded object might work, however I'm merely speculating here as a) I don't have access to an Office licence to test it myself, and b) I don't work on Confluence and as such don't have an intimate knowledge of it's workings.
If you're unable to make this work with an embedded object in your word document, then I suspect that it's unfortunately not possible within Confluence.
@Krupal Jawanjal when you Embed an Excel Sheet into a Word document the Excel sheet becomes a reference inside the document. The system you are opening the Word Document from would need access to the file system where the Excel document is saved. Since you are moving the Word Document to cloud storage, Confluence will not be able to access and open the embedded Word document.