Sam Allardyce said his young West Ham United side will learn from the experience of Sunday's 5-0 FA Cup with Budweiser third-round defeat at Nottingham Forest.

Injuries and a packed fixture list, including a Capital One Cup semi-final first leg at Manchester City and Barclays Premier League trip to Cardiff City this week, forced the manager to blood a host of youngsters at the City Ground.

A Hammers team containing three debutants and two other Development Squad regulars gave the Championship high-fliers a stern test for more than an hour, only for the hosts to score four times in the final 25 minutes.

After falling behind to Djamel Abdoun's early penalty, Big Sam saw his players battle back and enjoy a dangerous spell around the hour-mark. Just when it looked like the Hammers could grab an equaliser, Jamie Paterson drilled in a second.

With youth-team defender Reece Burke and Development Squad players Matthias Fanimo and Blair Turgott also introduced from the bench, the young Hammers conceded three more goals in the closing stages - two more to Paterson and one to Andy Reid - to give the final score-line an unfortunately one-sided appearance..

"We were having our best spell attacking-wise and I always say to young lads, when you're having a few sustained attacks, you have to be careful about it because if you don't score and take full advantage at that time you have to make sure you don't leave the back door open," said Big Sam. "I think it happens at first-team level sometimes and it happened on Sunday.

"When we allowed the second goal to go in, which was probably against the run of play at that time, they didn't do themselves any favours with the way they approached the tie after that, going all guns blazing on the all-out attack, making it very easy for Nottingham Forest to run through us and score more goals. That was the disappointing thing for me - not the first hour.

"I thought everybody stuck to their task and tried to play to their best and put a huge amount of effort in. We all know how many young players we had out on the field which gave Forest an advantage as they played their Championship side that played week-in and week-out.

"In the end it over-ran them by the fact the young players got lost at the end and didn't realise that, at 2-0, the most important thing was to make sure that Nottingham Forest didn't score another goal. We needed to try to play our way back into the game and stabilise the situation, but they didn't do that."

The magnificent 3,000-strong travelling support continued to sing until the very end, despite seeing their unfamiliar-looking team defeated.

The manager said he took no joy or pride whatsoever in overseeing a defeat, but pointed to this week's semi-final and the need to secure Barclays Premier League safety as the reasons for his team selection on Sunday.

"The big picture is that my hands were tied in the selection process regarding who I could pick. My hands have been tied nearly all season, because a lot of my players have not played even a third of the season so far due to trauma and other injuries.

"We know what the problem is and we've got to overcome the problem as quickly as possible.

"Nobody wants to get beat and we certainly don't want to get beat 5-0, but at the end of the day the semi-final against Manchester City is more important than this game.

"More managers change their team for the FA Cup than don't. Billy Davies didn't change his team, but he is one of very few. Most managers, even from the Championship, will change their team for the FA Cup third round.

"Managers change their team in the Capital One Cup as we did this year to good effect because we've got to the semi-finals.

"It would have been impossible to play the same 14 players on Sunday, on Wednesday and next Saturday at Cardiff, because that would have promoted us getting more injuries than we have already got.

"Circumstances were against me and I had to play the young players. I told everybody very early, so everybody knew what was going to happen. I was hoping the players were still going to stand up and make a better game of it, but unfortunately they didn't.

"Manchester City played on Saturday and we had to play on Sunday. I still needed to use Ravel Morrison, Modibo Maiga and Matt Jarvis and they played the whole game, while I brought Stewart Downing and Alou Diarra off as I need them as well.

"We also have the lads at home who are fit and they will all get themselves ready and prepare for the big, big game on Wednesday."

Finally, the manager confirmed again that the Club are working hard to bring in new recruits to bolster the injury-affected squad.

"We're still looking in the market to sign more players if we can. It's a critical situation at the moment and there nobody aware of it more than me, how desperate our situation has become over the last few weeks.

"With our position in the league, we have all got to stick together and get people back in the side with the experience and the quality and determination I know they have got to secure our Premier League status and get to the Capital One Cup final."