However, after making good progress in the past fortnight the England international expects to be back in action ahead of schedule.
"I had the operation nearly two weeks ago and things are looking good. Hopefully, I could be back even sooner than the six weeks," Richards told the Manchester Evening News.
"The operation was something that couldn't be avoided. I played in the derby at Old Trafford with it hurting and in the second half picked up an ankle knock as well so I was a wreck by the end of the game.
"After the Everton match the knee was swollen like a balloon and I couldn't carry on really. The medical advice was to get it done before the end of the season and that is what I did. It is for the best in the long term.
"I hate missing games, especially at such a crucial time but I will be giving it 100 per cent to be fit as soon as I possibly can. I will be back and I will be back with a bang!"