Merson wrote in the Daily Star Sunday: "What they are doing to him is disrespectful.
"He is one of the best midfielders of the modern age, a goalscoring phenomenon who has given everything for that club.
"To try and force him out like this is an absolute joke. I think he will go in January - and I'm shocked by that.
"Chelsea must be mad to let him go. They are already short in midfield, and things will soon get worse.
"If you're Chelsea, I just don't see how you fail to keep Lampard. It's ridiculous. He has been such a big part of that club."