However, Mick McCarthy, the Irish manager, refuses to say if this is the end for the 37-year-old Derby defender. McGrath won the last of his 83 caps in the scoreless draw with Wales in Cardiff in February.
"I have spoken to Paul several times this week and he agrees with the decision as he is still suffering with injuries," McCarthy said.
"Paul can play in one game and miss the next one. In the long term he wants to clear up these injuries. The more games Paul misses, the less chance he has of playing," McCarthy said.
Earlier this month McGrath was withdrawn from the Irish squad in controversial circumstances just half an hour before the team flew to Skopje for the 3-2 defeat by Macedonia. An Achilles tendon injury was the official explanation.
The Sunderland striker Niall Quinn, just back from a cruciate ligament injury, was not named in the squad which will be reduced to 20 before travelling to Romania. But McCarthy has indicated that there could be a late call for Quinn if he shows full match fitness in forthcoming club games.
Meanwhile there is a first call-up for the 17-year-old Everton defender Richard Dunne and recalls for Gary Kelly (Leeds), Curtis Fleming (Middlesbrough), David Savage (Millwall) and David Connolly (Watford).
With both Jason McAteer (Liverpool) and Alan McLoughlin (Portsmouth) serving suspensions, McCarthy has recalled the 35-year-old Crystal Palace midfielder Ray Houghton. "It was an inept performance against Macedonia. Even a point against the Romanians would be welcome," McCarthy added.
With Romania top of the table after five games and five wins with 19 goals scored and none conceded, it promises to be an uphill task for the Irish to restore their pride in Bucharest in the hope of qualifying for a third successive World Cup finals.
A one-match suspension rules out Liverpool's Mark Kennedy for the Republic of Ireland's European Under-21 Championship qualifying tie against Romania in Bucharest on 29 April.
But the ban has not prevented Kennedy being elevated to the senior squad for the following day's World Cup tie as suspension at Under-21 level does not apply to World Cup games.
Ian Evans, the Under-21 manager, will also be without Tottenham's Stephen Carr because of suspension as the Irish youngsters attempt to build on their 4-0 victory over Macedonia earlier this month.
The debutants in the squad are Neale Fenn (Tottenham), Owen Coll (Bournemouth), Peter Gain (Tottenham), Shaun Carey (Norwich) and Tony McDonnell of UCD, the only League of Ireland representative.
REPUBLIC OF IRELAND SQUAD (v Romania, Group Eight World Cup qualifying tie in Bucharest, 30 April): A Kelly (Sheff Utd), Given (Blackburn), Irwin (Man Utd), Cunningham (Wimbledon), Breen (Coventry City), Harte (Leeds Utd), Fleming (Middlesbrough), Kenna (Blackburn), G Kelly (Leeds Utd), Phelan (Everton), Dunne (Everton), Staunton (Aston Villa), Houghton (Crystal Palace), Keane (Man Utd), Townsend (Aston Villa), Savage (Millwall), Moore (Middlesbrough), Kennedy (Liverpool) D Kelly (Sunderland), Connolly (Watford), O'Neill (Norwich), Goodman (Wimbledon), Cascarino (Nancy).
REPUBLIC OF IRELAND SQUAD (v Romania in the European Under-21 Championship qualifying tie in Bucharest, 29 April): Murphy (Wimbledon), O'Connor (Huddersfield), Worrell (Blackburn), Quinn (Crystal Palace), Maher (Tottenham), Finnan (Notts County), Boland (Coventry), Farrelly (Aston Villa), Kilbine (Preston), Fenn (Tottenham), Foley (Wolves), Delap (Carlisle), Mahon (Tranmere), Inman (Peterborough), Coll (Bournemouth), McDonnell (UCD), Gain (Tottenham), Carey (Norwich).