The Hoops have refused to give up hope of persuading the Tottenham striker to return to the east end of Glasgow after he netted 12 goals in an impressive loan spell last term.
Fortune felt the arrival of Keane in the second half of the campaign boosted his own form in what he admits was a difficult first season at Celtic and he now hopes a deal can be struck.
"Of course I would like to see him back here," he said.
"Robbie is a star player and I really enjoyed playing with him and I think we did well together.
"I think the club has a lot of targets and we need players for the group. Robbie is a player who would be welcome.
"One player cannot make all the team, it's not one player who decides the issue of the season.
"It's the whole team, the whole group, and Robbie would be part of that group. If we all do well, we can do well this season. Of course, if we add good players it can only be good for Celtic.
"Celtic is a big club so they need big names."
Assistant manager Johan Mjallby revealed that boss Neil Lennon is still hopeful Keane could return for another temporary spell.
He said: "I don't know Tottenham's thinking when it comes to Robbie. He is out of our reach when it comes to buying him. But a loan would be perfect for us."
Regardless of whether he will have the opportunity to play alongside Keane again, Fortune is confident he will have more to offer in the season ahead now that he has had 12 months to settle in Scotland.
He said: "Personally, I know I have to score more goals than I did last year. I will work on it and try to do better than last year.
"First of all I will try to do more for me because I try to progress every year. Last year was a difficult year; this year is the year of Celtic.
"I learned a lot because I didn't know anything about Scottish football when I arrived. It's more difficult than everyone expects when they arrive.
"You have to fight every game and it's not easy. I'm ready to fight. Now I know it's a difficult league and I'm ready for it.
"I know the teams that I play against now. When I arrived, I didn't know teams like Falkirk but now I know the teams. I'm more confident and I'm ready now."
Celtic are likely to be linked with other forwards ahead of the new campaign as Lennon bids to bolster his squad but Fortune is not worried.
He said: "My personality is that I am always relaxed. There is competition but it's good competition so I like that."