No one expected David de Gea to play against Liverpool. He got injured in Span's match against Sweden and Solskjaer confirmed that he wouldn't play a part.
In fact, the Norwegian manager assured that Sergio Romero would be between the sticks against Liverpool. "He has trained really well. He looks fresh and in shape. He has played a couple of times and has shown that he is ready", he said.
Thus, David de Gea's miraculous recovery (he injured his hand) made sure Manchester United had their best keeper available for a key and important match against one of their rivals, Liverpool.
Someone who won't play any part is Paul Pogba. The French CM has a foot injury that makes him unavailable for selection.