Sir Alex Ferguson
Manchester United manager Sir Alex Ferguson.

Sir Alex Ferguson has shouldered responsibility for Manchester United's defeat by Ajax in the Europa League on Thursday.

The United manager admitted he took a "big risk" by playing an inexperienced defence at Old Trafford, as the home side progressed into the last-16 on aggregate, despite losing the match 2-1.

Manchester United cruised into a 3-0 aggregate lead courtesy of Javier Hernandez's clinical finish in the sixth minute.

But Aras Ozbiliz levelled for the visitors before halftime and Toby Alderweireld's late header ensured a nervy finish for United.

"I must say, I've got to accept I'm responsible for picking the team and I picked too many young players in the back four positions," Ferguson is quoted on the BBC. "It was a big risk I took."

The Manchester United manager opted for Phil Jones, Chris Smalling, Rafael and Fabio in his back-four and Ferguson acknowledged his side will have to improve, with Athletic Bilbao waiting in the next round.

"They all have great potential but on European nights you need experience in the back positions and it just made it a nervy night for us," Ferguson told MUTV.

"It was very nervy at the end of the game," the Manchester United boss added. "We didn't play well in the second half and they were by far the better team. I accept responsibility myself because I picked a team with too many youngsters in the back four positions.

"You play Ajax and know that they can keep the ball all night. The problem is that they don't really have a great deal of penetration. But they're all good young footballers, they are a growing team."

United crashed out of the group stages of the Champions League earlier this season but Ferguson cautioned that his side would not take their Europa League commitments lightly.

"In fairness, we have been changing the team around a bit," Ferguson said. "When we play Athletic, I think you'll find it will be a far more experienced team. Their home record is very good and we expect a very difficult game.

"That will be more of a challenge for us in the sense that getting the result in Ajax put is in a comfort zone, whereas we'll have to get the edge here before going to Bilbao."