The legendary Celtic captain is linked with a move away from Parkhead.
The 33-year-old is heavily linked with a move to Western Sydney Wanderers, though The Scottish Sun reported last week that Brown had rejected the A-League club's first offer.
Brown, who joined Celtic for £4.4 million in 2007 [The Guardian], has established himself as one of the club's all-time great players, having won 17 major honours during his 12-year spell.
But despite a phenomenal 2017-18 campaign, which saw Brown help the Hoops to another domestic treble and a number of end-of-season individual awards, the former Scotland skipper's role at Parkhead is being questioned after Callum McGregor usurped him as Brendan Rodgers's midfield anchor in recent months.
Nevertheless, Brown remains a huge influence off the field, and Forrest, his team-mate for nine years, admits that it would certainly be odd if the legendary midfielder left Paradise.
“Ever since I have been here there have been different changing rooms and he has always been there, he's kept everyone together," Forrest told The Glasgow Evening Times.
"You maybe hear different stories from different teams and how they work but Broony is massive in that part as well that people maybe don’t see.
“For me, he has always been the captain, the main man, and if he did leave for me it definitely would be strange. He’s great with young boys and new signings as well. He’s invaluable I would say."
Brown is out of contract at Celtic this summer and although an extension will be tabled, it remains to be seen whether Rodgers can get him to sign it. The longer it goes, the less likely a signature is.