Sir Alex Ferguson accused his Manchester United players of failing to understand the importance of the FA Cup after the 11-time winner struggled to reach the sixth round at the expense of non-League opposition.

The Premier League leader was given an uncomfortable time by Crawley Town before edging past the team from the fifth tier of English football 1-0 at Old Trafford on Saturday to book a quarterfinal spot.

But United's victory came at a cost as Anderson, Rafael da Silva and Fabio da Silva were injured and are now all doubtful for Wednesday's Champions League game away to Marseille.

Ferguson made his feelings clear after his players failed to perform.

Although the likes of Edwin van der Sar, Patrice Evra, Nemanja Vidic and Dimitar Berbatov were given the afternoon off, the likes of Bebe, Michael Carrick and Gabriel Obertan failed to impress.

"Some players came in and didn't do themselves justice. No doubt about that," said Ferguson.

"In the second half, we weren't at the races. It was disappointing. We might have some players who don't understand what the FA Cup is all about. That is the biggest lesson for them."

Anderson suffered a hamstring problem while brothers Rafael and Fabio da Silva also suffered knocks.

Ferguson said he will assess them before deciding whether they are capable of making the midweek journey to France.

"It was a big problem, having to take our two fullbacks off and Anderson with his hamstring," added the United manager.

"It unbalances the team. We will assess them on Sunday. We had to play Darren Fletcher at right-back and he did well, but it didn't help."

Ferguson was full of praise for Crawley, who was denied a replay when substitute Richard Brodie hit the woodwork in stoppage time in front of their 9,000 travelling fans at Old Trafford.

"All the criticism about the FA Cup, it tells you what it means to a small club like Crawley," added Ferguson.

"They showed more desire in the second half. They made it very difficult for us. We were second to every ball. They could have equalized. They deserved a draw really. We never had a shot at goal in the second half.

"First half we did very well, no complaints. We could have been three or four up. It wasn't to be and if you are only 1-0 up in a cup-tie it only takes a second to lose a goal, and we nearly did."

Crawley did not leave Old Trafford completely empty-handed. They will make more than 1 million pounds ($1.6 million) from the tie from television rights and gate receipts from a sellout 75,000 crowd.