Manchester City boss Manuel Pellegrini says he "would do exactly the same again" after playing a weakened team at Southampton, with Wednesday's game against Real Madrid in mind.
"I think we could've played on Saturday and named a stronger team," Pellegrini told BBC Sport.
"But we had to prioritise Wednesday."
He said: "We continue in the Premier League in the next two games to be in the top four so that was a risk, but one we also had to take."
Star players Sergio Aguero, Kevin de Bruyne and Vincent Kompany were rested but 19-year-old Kelechi Iheanacho started, and scored twice.
Pellegrini, who is being replaced by Pep Guardiola at the end of the season, questioned his side's "motivation" and said: "The best way to prepare is to win but we couldn't do it.
"Playing with too many players that are not playing often is difficult. I expected more - especially defending. I'm very frustrated because I didn't expect that performance."
Madrid played their La Liga game on Saturday, beating Real Sociedad 1-0 to stay in the Spanish title hunt.
Pellegrini made a similar decision in February when forced to play an FA Cup tie with Chelsea three days before a Champions League match against Dynamo Kiev. They lost 5-1 to the Blues, but then won 3-1 in Ukraine.
'Champions League qualification still in our hands'
Pellegrini was not concerned by the fact Manchester United and West Ham have closed the gap on them in the battle for fourth place.
City are five points above United and six clear of the Hammers - but have played a game more than both their rivals.
He said: "It's exactly the same. It all depends on what we can do in these last two games. We are three points behind Arsenal and if we beat Arsenal we'll be in third position before the last game."