Here's a controversial hot take for you: Thomas Müller is a really good player. A really, very very good player. You wouldn't think it at first glance, but he is. He's no Messi, he's no Cristiano Ronaldo. He is unique. And he's awesome. Any team in the world would be lucky to have him. As it stands, only Bayern Munich are so lucky. Chances are they will be the only team to be so lucky.
For whatever reason, there's been a multi-month rumor going around that Manchester United might want to buy him. They probably do. They're not stupid. And maybe they're harboring a tiny bit of hope that Müller will eventually pull a Bastian Schweinsteiger and look for a new challenge or some such. I don't see how winning all the time gets boring, but that's just me.
So where do Chelsea come in? Probably nowhere, but the club and Müller are in the news today thanks to Bayern and Germany legend Lothar Matthäus, who decided to utter the following few sentences, at some place, at some recent hour, in some unknown context. I'm not sure those details matter.
"He does not need Manchester United or Chelsea. Barcelona perhaps could use him, but I do not know whether he can deal with their game."
"My opinion is that he should definitely stay at Bayern for his lifetime. He started his professional career at Bayern and I think he should end his career here. He does not need any new challenge as he is always playing at the highest level every year at Bayern."
-Lothar Matthäus, source: Mirror
And that somehow constitutes a Chelsea transfer rumor. And that's why we call it Silly Season.