Waterford's championship preparations have gone for bad to worse with the news that McGrath will definitely miss the Munster hurling semi-final with a broken thumb.
McGrath, who was already struggling to regain fitness following a knee injury, was injured while lining out for Mount Sion in a club match over the weekend.
The 2004 All Star is the latest in a long line of injuries and suspensions to beset the Waterford management team who have already lost John Mullane to a long-term injury while Eoin Kelly is currently serving a 12-week ban.
Paul Flynn is also out of action after his dismissal against Limerick although his four-week ban is due to expire before Waterford get their championship underway at the start of June against the winners of this weekend's clash between Tipperary and Limerick.