Fekir is expected to move on after president Jean-Michel Aulas said the club has reached "an understanding that he can go", with the France international linked to Liverpool and Arsenal.
Juninho, who arrived at Groupama Stadium in May, indicated that he has not given up hope of keeping hold of Fekir as the team's new head coach Sylvinho prepares to welcome him along with the rest of the Lyon squad for pre-season training.
"I would like Nabil Fekir to stay," Juninho told reporters. "He's a great player. He's got a lot of talent.
"We'll see what happens. I'm a fan of his talent. We'll see him tomorrow [Thursday]."
After welcoming Brazilian midfielder Mendes, who arrived from Lille in a deal worth €25m, Aulas outlined the club's intentions in the transfer market.
The Lyon chief named Sampdoria defender Joachim Andersen as a target and said the club are close to agreeing a deal to keep 15-year-old protege Rayan Cherki at the club.
"We're getting closer to a lot of central defenders, including Andersen," said Aulas.
"We're moving forward. With Rayan Cherki, we are close to an agreement."
Mendes, who made 66 Ligue 1 appearances during two seasons at Lille, explained compatriots Juninho and Sylvinho were integral in persuading him to come to Lyon.
"Lyon are one of the best teams in the world," he said.
"I'll give my best for this club. Juninho and Sylvinho told me about the project and I quickly joined. It's also a family choice.
"I would give anything for the team and for Sylvinho. I'm here to help the team.
"The coach will make me play in the position he wants. I can still make progress in many areas. I'm in Lyon to learn."