Davies swapped seven players from the 3-1 Championship win at West Brom for the FA Cup third-round replay against Birmingham at St Andrew's.
The Scot saw his side slip to a 1-0 defeat and lose their 18-game unbeaten run in all competitions but felt it was important to rest players ahead of another crucial match on Saturday.
"It was important to freshen up and rest people. We did that because we know what the priority is," Davies said. "We will have a very different side at the weekend, without a doubt. It will be a different look to the side when we face Reading.
"It was all about fitness, about getting ready for the remaining league matches. We wanted to make sure some players got a good run-out. That was the most important objective.
"We will sit down and talk about what we need to do on Saturday against Reading. We will get back to the important games that we have remaining and there will be changes, without a doubt."
Source: Team Talk