Sir Alex Ferguson admits he did not want to take the gamble of giving Nemanja Vidic back-to-back starts for the first time since September when Manchester United went to Real Madrid on Wednesday.
Vidic, 31, was not even named on the bench as Jonny Evans and Rio Ferdinand were paired in the centre of defence for the 1-1 Champions League draw.
The United skipper had been praised for his performance in Sunday's 2-0 win over Everton but Ferguson was wary of selecting the Serbian international - who has had knee problems over the past 14 months - for successive matches.
"Three days after Everton was a risk," Ferguson said.
Meanwhile, the Red Devils boss has revealed he will make wholesale changes for Monday's FA Cup clash with Reading.
"It's an incentive to get to the quarter-final. Whatever side I pick, I expect to qualify," he said.
Vidic is one of several players who could come into contention along with Tom Cleverley, an unused substitute in Spain. Despite the England international's omission on Wednesday, Ferguson still labelled him as "an important member of our squad".
Ashley Young, who has not featured in the last seven games, is in line to make his comeback, while others who could come into the starting line-up include Javier Hernandez, Ryan Giggs, Nani, Antonio Valencia, Anderson and Chris Smalling.
Ferguson scouted Reading on Saturday when Brian McDermott's team lost 2-1 to Stoke and he was impressed by their battling qualities.
"I went to see Reading last week and they're a team who are showing plenty of fighting qualities at the moment, as you'd expect given they're down the bottom of the league," he said. "We'll take nothing for granted. In the FA Cup you always expect the unexpected. It happens so many times. You just hope you're not a casualty or a shock. We've had a few over the years."
After Reading visit Old Trafford, United then face Queens Park Rangers and Norwich before the return leg against Real at Old Trafford on March 5, and Ferguson has vowed to carry on alternating his team.
"It's not easy to rotate but it has to be done," he said. "The biggest responsibility lies with myself in picking the right team."