The former Blues midfielder has joined Manuel Pellegrini's side on a short-term loan.
Some even went as far as claiming they'd 'disown' him if he did so.
Chelsea's loss, though, is Manchester City's gain this summer, as the 36-year-old Blues and England legend has been confirmed as a City player and pictured taking his first training session with Pellegrini's squad.
The deal is only a loan move, of course, with Lampard moving to the Etihad Stadium primarily to maintain his fitness levels ahead of the next MLS season, where he will ply his trade for New York City FC - a subsidiary of Manchester City.
The transfer, however, will disappoint Chelsea fans nevertheless. And City fans? Their reaction has been rather mixed.
There has been the inevitable smugness of some, who take pleasure in the emotional rollercoaster Blues fans have been subjected to.
Others have voiced their disapproval at signing a veteran who could struggle for game time within a City side full of world-class midfielders.
An overriding impression, though, was the feeling that seeing Lampard in a City shirt was simply 'strange' or 'weird'. The colour may be slightly lighter but the image still looks rather unfamiliar...
Oh Frankie, Frankie................... Welcome to Manchester :-) http://t.co/oFevurZyD6— Mark Anderson (@cityboy100) August 6, 2014
It may only be on loan, but I'm thrilled that one of my all time favourite players has joined city ! Welcome Lampard !! #mcfc— Chris Williams (@Dietmar29) August 6, 2014
Manchester City have made the signing of the season. Frank Lampard.— Lee Robert (@Lee_Badeedee) August 6, 2014
Frank Lampard is innovative football management, but as a fan I'd rather pass. He's 100% Chelsea. Will feel the same when he scores #mcfc— Charlie Raincock (@charlieraincock) August 6, 2014
I don't want frank lampard he will not help build city at all in my opinion— Wang (@zlanglois) August 6, 2014
Feels weird city signing Lampard— Callum (@EvansCallum) August 6, 2014
Lampard on loan, hahaha, Chelsea fans will be fuming