Manchester United manager Louis van Gaal says the recover of key players is a must ahead of the last part of the season.
The Red Devils will play more than 15 games until the end of the campaign if they continue to progress in the Europa League.
And the Dutchman admits it is not easy to prepare games when important players are out because of injury.
"We have to go step by step, I think," van Gaal said.
"We now have four victories in a row, which is fantastic, but we have a very small selection at the moment. Players are coming back, but I still have to solve a problem in my line-up every week.
"When players are coming back, they are not fit enough. You've seen how [Marcos] Rojo was struggling. I give them 20 minutes and then 50 minutes and today 70 minutes and I have to do that within Premier League matches.
"It is better to do that in the second team, but I am forced to do that. The last four matches have been great, but we still have to go step by step.
"We could still have 20 matches to go and we've already played 43 matches, so that's more than 60 matches. When I was trainer-coach at Bayern Munich, we played 55 including the final of the Champions League. It's very difficult to fulfill the expectation."