Filming is due to start in two months and Clooney is reportedly getting
increasingly desperate to get his best friend to commit to the project.
A source told Britain's The Sun newspaper: "Brad has not been able to
confirm 100 per cent that he will be available - and that's making George
very anxious.
"His best friend is out of the country and looking forward to being a dad
for the first time. But the movie is only weeks away now."
Pitt, 42, has barely been in the US since March - and has been spending
quality time with Jolie and her two adoptive children in Namibia.
The source added: "Instead of being there to work on the project, Brad is in
the middle of Africa. People are worried that he will prefer to carry on
being a dad rather than go back to work."

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