"It is important to have a strong squad, maybe even a massive squad," the Scotland captain told Manchester Evening News.
"You see what it is like when you are battling for three trophies. It got really tough towards the end last season.
"I think we had only 12 or 13 fit outfield players with first team experience. We had to win league matches and go and win Champions League matches away and FA Cup ties and it was difficult.
"You don't feel tired and you want to play in every game. But the manager knew that if he could have rested some players and rotated the squad better than he could have freshened up the team.
"We don't want to make excuses but Milan rested their whole starting XI before both their semi-final matches against us.
"They only wanted to win the European Cup last year because of their points deduction in Serie A. They set out to win that one trophy, and they achieved it, but we were challenging for three trophies.
"However, we were one game away from the Champions League final.
"We got to the FA Cup final and lost a close match and won the title so last season was a fantastic one .
"Last year we didn't have any injuries in the first half of the season then they all came at once at the end.
"You can't tell what is going to happen but the manager knows now he has a squad that can cope with injuries. We have experience there now."