The United squad did not include Ronaldo, Jadon Sancho, Harry Maguire and Phil Jones, after they participated in the loss against Wolverhampton Wanderers in the previous round of the English Premier League.
Maguire and Jones are also injured, but they are expected to return when they play at Aston Villa in the league next Saturday.
On Ronaldo’s absence, Rangnick said on Monday: “I spoke to Cristiano yesterday before training and he told me that he has had some problems in the past few days.”
He added: “They are minor problems, but in the end we decided that it was logical not to take any risk in a match that could easily extend to 120 minutes, so we decided to give him a rest.”
He continued, “He has some muscle problems in the upper leg. I don’t think it’s completely serious.”
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