The Eels winger is desperate to see his great mate return to NRL action.
Mitchell was the form player of the competition before succumbing to a calf injury in round 11 and hasn't played since.
The Rabbitohs centre has been seeing a specialist to get to the bottom of nerve-related issues in his back and has been ruled out indefinitely, meaning the 29-year-old won't feature in this week's Indigenous Round clash with Parramatta.
"I speak to him all the time and you don't wish injuries upon any player," Addo-Carr said.
"Everyone wants to play and train every week but that's the way it is at the moment.
"I'm always talking and making sure to check in on him and I know he's doing his very best to get back on the field.
"He's my brother boy and I hope he gets back soon."
Addo-Carr has formed a fearsome partnership with Mitchell over the years in the NSW State of Origin team and the Australian Test side.
And while his club's season is essentially over, Eels winger Addo-Carr will use Saturday's clash with the Bunnies at Allianz Stadium to further his chances of earning selection for this year's Rugby League World Cup.
Australia's dominance at international level has never been more under threat, with the rise of Tonga and Samoa and the re-emergence of a stacked New Zealand side.
Addo-Carr was taken on last year's Kangaroos tour by Kevin Walters but has not scored a try at NRL level since May.
"I've had a few phone calls with Kevvie and we have a close connection and I've always told him I won't let him down," Addo-Carr said.
"Hopefully I do get the call-up because I love putting that Kangaroo jersey on and when someone backs you - he gave me an opportunity last year - you don't want to let them down.
"The Aussie camp is the best camp to be a part of. The bonus is playing footy together.
"They (the other nations) can talk all they want, we just have to keep it humble and go about our business like Australians do."
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