James McClean has left the Northern Ireland squad to face the Faroe Islands after becoming the latest player to opt for the Republic of Ireland.
"My dream has always been to play for the Republic of Ireland," said McClean.
Warren Feeney has pulled out of Wednesday's Euro 2012 qualifier with a groin injury and is replaced by Linfield striker Peter Thompson.
Martin Paterson (thigh) and Josh McQuoid (hamstring) were ruled out of the Windsor Park game on Sunday.
Feeney suffered the injury while making his Plymouth Argyle debut on Saturday and withdrew from the squad after Monday's training session.
McClean has been in fine form for his club in the Airtricity Premier Division.
The likes of Darron Gibson, Shane Duffy, Marc Wilson and Daniel Kearns are among those to have taken advantage of a ruling which allows players from Northern Ireland to choose which national side they represent, provided they have not played in a competitive senior international.
Although Worthington hopes to add Alex Bruce - twice capped by the Republic in friendlies - to the Northern Ireland ranks, the IFA have publicly bemoaned that the ruling has had a destabilising effect on them.
"I appreciated the call-up to the senior team having played at U-21 level," added McClean.
"I think Nigel understood where I was coming from and I think he appreciated the phone call.
"I don't want to be tied up internationally at this stage of my career and I'm prepared to take a risk in that regard."
Worthington is concentrating on Windsor Park clash after the loss of the trio.
"It is disappointing to lose players ahead of an important qualifier, but our focus remains on Wednesday night and the players available for the game against the Faroe Islands," he said.
McQuoid suffered a knock in training which ruled him out of Millwall's season opener against Reading.
Paterson had been included in the squad for the first time in a year but came off injured at half-time during his side's game against Watford.
"Martin said he couldn't play to his full potential so he had to come off - he won't go with Northern Ireland now," said Burnley manager Eddie Howe on Saturday.
"We need to make sure we get him 100%.
"I wouldn't say it was a recurrence of any injury but Martin was just not feeling 100%.
"He has done all his pre-season and been fine, so it came as a bit of a surprise because I thought he looked quite sharp in the first half against Watford."
With Kyle Lafferty ruled out, Paterson would have been vying with David Healy, Peter Thompson and Jamie Ward for starting berths up front against the Faroes on Wednesday.
Healy, Northern Ireland's record goalscorer, has been recalled after being left out of the squad for the Nations Cup games against the Republic of Ireland and Wales in May.
Paterson and Ward also earned recalls, but manager Worthington's striking options have now been further limited.
St Johnstone keeper Alan Mannus replaces injured Maik Taylor.
Healy's Rangers club-mate Lafferty is sidelined after undergoing a hernia operation while Chris Brunt is ruled out by suspension.
Mannus, who recently moved from Shamrock Rovers to St Johnstone, takes one of the three goalkeeper slots with veteran keeper Taylor ruled out for the game at Windsor Park by a shoulder injury.
Derby County striker Ward has been on the bench for four Northern Ireland games but has yet to earn a cap.
Burnley forward Paterson has not featured for Nigel Worthington's side since coming on as a substitute against Montenegro last August.
Northern Ireland head into the match second bottom of Group C - two points above the Faroes - having picked up six points from their first five games.
They lie five points behind second-placed Slovenia but have games in hand on all their rivals.
Northern Ireland squad
Goalkeepers - Tuffey (Inverness Caledonian Thistle), Camp (Nottingham Forest), Mannus (St Johnstone)
Defenders - J Evans (Manchester United), McGivern (Manchester City), Cathcart (Blackpool), McAuley (West Brom), Hughes (Fulham), Hodson (Watford)
Midfielders - Baird (Fulham), McCann (Peterborough United), McGinn (Celtic - on loan at Brentford), Gorman (Wolves), C Evans (Hull City), Davis (Rangers), Clingan (Coventry City), McCourt (Celtic)
Forwards - Thompson (Linfield), Healy (Rangers), Ward (Derby County).