The 30-year-old is out of contract in June 2021, with manager Mikel Arteta admitting it is imperative the club keep their star striker.
And Sagna has warned the Gunners will find it hard to replace the Gabon international, just like when they allowed his former teammate Robin van Persie to leave.
"He can't go now because Arsenal are on the way to building something strong," Sagna exclusively told Goal. "They can't afford to lose him. If they have to pay him, then just pay him because if they want someone else of his quality they cost £150m.
"So don't spend this £150m, just spend £50m and give it to him. It's the same as van Persie and I think you have to learn from that situation.
"Auba deserves it. I'm not saying that because of his name or because he has scored a few goals. He's the best striker in the league."