McIlroy saw his side fall to a rare defeat as the Millers hit three times, but the former Northern Ireland boss still believes wins in the remaining two games could be enough to secure a play-off berth.
"I'm very disappointed with the defeat and with the goals we conceded," said McIlroy.
"But to be fair Rotherham are a very good side and I'm glad our lads gave it a good go as we looked for a win.
"We're still in there fighting and we will continue doing that until the end of the season.
"If we win our remaining two games I believe we are still in with a great chance of the play-offs."