Please be warned this is speculation but we have two reports of Madden coming to Stadia on August 28. The first report is from Reddit user nichostetler who posted a picture of interaction with EA rep and they said Stadia version is coming the same date as other platforms. There is also a Newsweek article dated July 1st which states that it is coming that date as well.
My feeling is this is a mistake and there will be clarification shortly. If Madden was due to release this week on Stadia I also believe we would have known by now. There is also the Madden official site which does not list as Stadia is coming on August 28.
File this under extreme doubt.