Inline citation within my inline citation (MLA)
According to the MLA style detailed here you can use the following for inline citing as per the example you gave. 


  Citing indirect sources
  
  Sometimes you may have to use an indirect source. An indirect source is a source cited in another source. For such indirect quotations, use "qtd. in" to indicate the source you actually consulted. For example:
  Ravitch argues that high schools are pressured to act as "social service centers, and they don't do that well" (qtd. in Weisman 259).
  
  Note that, in most cases, a responsible researcher will attempt to find the original source, rather than citing an indirect source.


So from the information you gave, your cite would be (qtd. in My Source Author pagenumber)

It may also be of benefit to enquire if your department have a style-sheet that would give guidance on referencing.