Romelu Lukaku was widely expected to leave Everton for Chelsea earlier in the summer.
The Belgium international had been earmarked as a priority signing for the Blues, with manager Antonio Conte ordering Roman Abramovich to get a deal done.
However, in a stunning transfer twist, Lukaku ended up joining Manchester United for £75million instead.
The striker is already up and running for the new season, bagging a consolation as the Red Devils lost 2-1 to Real Madrid in the European Super Cup earlier in the week.
Chelsea have since smashed their transfer record by signing Alvaro Morata from Real Madrid in a £70m deal.
And Merson thinks the Spain international is a better fit – believing Lukaku does not have the intelligence to play alongside Eden Hazard and Cesc Fabregas.
“Alvaro Morata is a top player but how long will it take him to settle?” he told the Daily Star.
“I don’t think Chelsea missed out on Romelu Lukaku. Morata is a better fit for them. But he’ll need time to adapt to English football.
“Lukaku’s not bright enough to play with Eden Hazard and Cesc Fabregas.
“He needs the ball over the top, and he’ll get that at Manchester United.
“But I still don’t think United have enough to open teams up. They don’t have enough guile.”
Lukaku is expected to start when United face West Ham at Old Trafford on Sunday (4pm).