"Laurent is going to Paris because we've agreed to let him have the operation over there," said Sir Bobby.
"He's going to stay there for a week because he can't train at all.
"I would expect he'll be out for a minimum of three to four weeks and possibly five. I'm very disappointed because we know what Laurent can do for us.
"It's a bit of a disaster really."
Robert himself is disappointed to be missing so many important games, commenting: "Logically I will be out for a month. It is disappointing to miss the Arsenal game tomorrow and then the Champions' League match with Feyenoord in Holland on Wednesday.
"I did think about trying to play on but if I got another knock on the injury it could be really serious and it is sensible to have the operation."
Hugo Viana will deputise for Robert on the left, but the club will look into the possibility of hastening the Frenchman’s return by him wearing a protective mask to play in.
Several high profile players have done this before, including Gazza and Sinisa Mihailojvic, and Trevor Sinclair is expected to play for West Ham wearing such a mask this weekend, only eight days after fracturing his cheekbone.
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