By Alan Hansen BBC Sport football expert

If the management decide to try a three-man defence again, I can only see it contributing to England's downfall

There is no doubt for me that England's game in Israel on Saturday is a must-win.

Steve McClaren has already seen his squad hit by injuries and the fixture congestion has not helped him at all - but none of that will be taken into account if England get a bad result on Saturday.

There will be no hiding place and no excuses. That's the way it is when you are England manager.

It really doesn't matter about the performance. All they need to do is go there, get a result and get out.

If that happens, it will alleviate the pressure on the manager and the players.

The defence could be key.

With Gary Neville out and Jamie Carragher set to start, McClaren could be tempted to opt for a three-man defence.

For me, that could be catastrophic.

They tried it against Croatia and it was a shambles, and let's not forget the personnel involved then were Carragher, Rio Ferdinand and John Terry: three top-class centre-backs.

They aren't used to the system and, even worse, they aren't used to each other.

You're going into the unknown and this is not a game for the unknown - just like the Croatia game.

In Zagreb, you could see the system wasn't working right from the word go and if the management decide to try it again, I can only see it contributing to their downfall.

SATURDAY'S GAMES Rep of Ire v Wales (1500 GMT) Scotland v Georgia (1500 GMT) Israel v England (1830 GMT) Liechtenstein v N Ireland (1915 GMT)

Like England, Scotland will be looking for three points in their Euro 2008 qualifier against Georgia at Hampden as Alex McLeish takes charge for the first time following Walter Smith's departure.

I think Alex is the right man to continue the good work started by Walter, who engendered a tremendous team spirit and work ethic in the squad.

Under Walter, the Scotland players went on to the pitch believeing they could compete and that hadn't happened for a while.

That belief was reflected in the results they had, capped by the magnificent win over France.

If Scotland can get four out of six points from the home game against Georgia and the visit to Italy the following Wednesday, that would be a fantastic.

First things first, they must beat Georgia to get Alex off to a great start in the job and to keep the belief that they can qualify for Euro 2008 - which would be a truly amazing achievement.

Elsewhere on Saturday, the Republic of Ireland host Wales in a massive game for Steve Staunton.

I played alongside Steve at Liverpool and I know he's up to the task. He's a tough character and he won't shirk from anything.

I just hope the team and the country get behind him and they gets a decent result.

Of course, Wales boss John Toshack is another old team-mate of mine so I have to stay neutral on this one... I'm hoping for a draw!

Finally, Northern Ireland have had some unbelievable results in their qualifying campaign, not least the win over Spain.

Lawrie Sanchez's side travel to Liechtenstein on Saturday and a win there will maintain their belief they can qualify for Euro 2008.