Much of the attention had been on Mortlock, with Gerrard shirking any kind of send-off from the Melbourne faithful in their final home game of the season.
At the end of their 32-17 loss to Queensland at AAMI Park, the former Wallaby confirmed he would leave the Rebels and return to Japan to play out his career.
"At the stage I'm at in my career, it was just too good an offer to refuse," said Gerrard who has played 24 Tests for Australia.
"We're going to spend a few years there and then move back to Sydney."
After starting his career in NSW in 2001 and then at the Brumbies, he moved to Japan for two years in 2009 before re-igniting his Australian career in Melbourne.
The 29-year-old was one of their most talented, consistent and versatile performers as he passed a milestone ton of Super Rugby caps.
Gerrard plans to play one of the Rebels' two upcoming games in South Africa to finish the season and then return for the birth of his fourth child in Sydney where his family are building a new home.
"He's been one of our best players," said Melbourne coach Damien Hill.
"We'll miss him ... he's been a leader, he's covered fullback, wing and outside centre for us and he's got one of the best kicking games in the whole competition."
The Rebels would have liked to have kept Gerrard but Hill said they couldn't compete with the money on offer in Japan.
"He's at a stage of his career where that really matters.
"We fully respect his decision - we're lucky to have had him for the time we have."
The Rebels leave on Sunday for games against the Lions in Johannesburg and then the powerful Stormers in Cape Town.
Star back James O'Connor is set to miss the trip after re-injuring his hamstring in the loss to the Reds however Mortlock, who has been battling a calf problem, is a certainty to travel.
Lloyd Johansson will come into the squad for O'Connor.
Hill said it would be a tough tour.
"We haven't won a game in South Africa," he said.
"If we put the same effort in (as we did against the Reds), we're going to be on the wrong end of the scoreboard.
"We need to improve."