Goalkeeper Mark Schwarzer will miss Middlesbrough's bid for European glory after undergoing surgery to repair his fractured cheekbone.
However, the 33-year-old should be fit to take his place in the Australia squad for this summer's World Cup finals.
Schwarzer was due to have an operation to repair the damage in Darlington this afternoon following his clash with West Ham striker Dean Ashton during yesterday's 1-0 FA Cup semi-final defeat at Villa Park.
He could be back in light training wearing a protective mask within a fortnight, but he will be unable to play again for around a month.
Head physio Grant Downie told the club's website: 'Mark is likely to miss the rest of Middlesbrough's season, but should be okay for the World Cup.'
The injury will rule Schwarzer out of Thursday night's UEFA Cup semi-final, second leg clash with Steaua Bucharest at the Riverside Stadium.
Had it not been for his performance in Romania last week, the Teessiders could have been facing a 3-0 rather than 1-0 deficit going into arguably the most important 90 minutes of the season.
'Mark Schwarzer made two very important saves,' McClaren admitted later. 'I thought their goalkeeper made two very good saves, but Mark, certainly in the second half, kept us in the tie.'
With the final taking place on May 10 in Eindhoven, he would be unlikely to be available should they progress.
However, while he may also struggle to make his country's friendly clash with Greece on May 25, he should be fit for the warm-up games against Holland and Liechtenstein which precede their opening Group F match against Japan on June 12 in Kaiserslautern, where he played Bundesliga football before his move to England.
Schwarzer's absence will come as a huge blow to Boro with his form, particularly in Europe, having helped them make something of a season which has alternated between expectation and frustration.
Ironically, he might have left the club he joined in a £1.5million move from Bradford in February 1997 during January as unrest festered within the camp.
He submitted a transfer request despite being told he was wanted on Teesside as Boro attempted to offload Ugo Ehiogu and Jimmy Floyd Hasselbaink.
However, he later withdrew it and has impressed both his manager and the fans with his contribution ever since.
Compatriot Brad Jones, the man who was eventually beaten by Marlon Harewood's 78th-minute strike as the Hammers ended Boro's FA Cup dream, will deputise with youngster David Knight likely to occupy the bench.