The 71-year old Scotsman will retire as Manchester United boss at the end of the season and will bow it with a huge number of people praising him for a remarkable career, including the Galaxy pair who felt his exploits will never be matched.
"Arguably the best manager of all time. A legendary career," said Arena.
"I actually sent him a note - I don't know if he'll get it, but I congratulated him on his career, his retirement, everything he's done, and offered him the opportunity to visit LA anytime he wanted."
"It's going to be a big loss to the game. In Manchester, everybody will miss him. I'm sure in the Premiership it's the same thing because there's respect from every coach and every player around the world."