Not good enough, admits Raynor
They struggled to find a way through Edgar Davids' well organised visitors and fell 2-0 to strikes from Jake Hyde and substitute Andy Yiadom.
It was the Millers' second defeat on the spin, following last week's FA Cup reverse at Aldershot, and saw them drop out of the automatic promotion frame in League Two ahead of Saturday's trip to Oxford United.
Assistant manager Paul Raynor offered no excuses and said changes were on the cards.
He said: "I think at the moment we could make ten or 11 changes for Saturday but we'll look at it, study the DVD, take what positives out of it that we can and look where we can improve because that was just not good enough.
"We had enough possession but didn't do enough with the ball or create clear cut opportunities. We were very disappointed with the result and the performance.
"Individuals need to look at themselves and we as a management team need to look at ourselves and what we could have done differently.
"It's not about who is hiding behind the players. We are all doing this together."
Raynor added: "We're bitterly disappointed because our league form has been reasonably good. Before the Aldershot game we were playing really well but we've had two bad defeats so we will have to take it on the chin and put it right."