Liverpool will be hoping that, after playing out a thrilling 3-3 draw over the course of 120 minutes and enduring the knife-edge tension of spot-kicks, Blackburn's players will be both physically and mentally fatigued for the match at Ewood Park.
But McDonald is confident the squad are ready for their second encounter with a 'big four' side in four days though and is expecting a similar performance.
"Preparations have been really good," McDonald said.
"They have rested, eaten, rehydrated. They have had plenty of massage, had a little bit of the ball, and we will do a lot of work in the video room on Liverpool's strengths and weaknesses.
"They are fine - they know how to recover and they are very fit. I think they showed that in the really strong way they finished off the game against Stoke the Saturday before.
"They then competed against a top-four team in Chelsea and were excellent over the course of 120 minutes, so I wouldn't expect anything less than a good, strong-running performance - as well as a good football performance - on Saturday."
Although on paper it looks demanding, McDonald claims he was pleased to see another big side to come to Ewood immediately after Chelsea as it will ensure the players retained their focus.
"It is probably better that we are playing Liverpool after a great experience during the week, because we have to be on our guard," McDonald said.
"If we are not, they will punish us and the players know that. It is a huge game whenever Liverpool are in town there is always a big crowd and a fantastic atmosphere.
"That makes the players work that little bit harder, concentrate more and play even better football."
After a run of only one win in 10 games, Liverpool have stopped the rot in recent weeks with victories over Debrecen in the Champions League and Everton in the Merseyside derby.
McDonald is under no illusions about the threat Rafael Benitez's team will pose, but believes Wednesday night demonstrates that at home, Blackburn need not fear anybody.
"They (Liverpool) can't be underestimated," he said.
"They have got some fantastic players and we have to play 100% like we did the other night. If we do that, we have a chance of winning.
"It is always special to play one of the big four and Liverpool are certainly one of them.
"They have come out of a little rut with a couple of good results and they will be coming here trying to take three points to close that gap at the top of the league.
"But they are going to have to play well, because we are at home and our home record is fantastic."
Liverpool 8/11, Draw 13/5, Blackburn 4/1