Damien Johnson could miss the rest of the Euro 2008 qualifiers

Birmingham City midfielder Johnson is also likely to miss the last two qualifiers against Denmark and Spain after suffering a new hamstring injury.

Burnley defender Duff is definitely sidelined for the rest of the campaign because of a serious knee injury.

Keith Gillespie (hamstring) is a "major doubt" for the trip to Sweden.

Gillespie was forced off midway through the first half of the 3-3 draw at Bramall Lane on Tuesday night.

The former Manchester United and Newcastle United player received treatment on Wednesday morning but it will be 48 hours before the full extent of the injury is known.

Johnson will be sidelined for up to a month after his latest hamstring injury.

The 28-year-old had just returned to fitness after missing the opening six weeks of the campaign with a hamstring problem suffered in a pre-season friendly at Walsall.

But a scan has revealed he tore the other hamstring during Monday's reserve team outing with West Ham.

Duff sustained a cruciate ligament injury against Crystal Palace at the weekend and is out for the rest of the season.

Northern Ireland take on Denmark at Windsor Park on 17 November and end the campaign in Spain four days later.