The former Schalke player is coming towards the end of his fourth year at Manchester City.
He looked set for a switch to Bayern last year before suffering a major knee ligament injury in the Community Shield against Liverpool in August.
Having battled his way back to fitness, Bayern are again looking set for an attempt to land the 24-year-old.
"He doesn't match up at all to Bayern, in terms of character. He's an inconsistent player, who is very withdrawn," Sagnol told French radio station RMC.
"For me, he isn't made for this club.
"He's got lots of problems, at Manchester City and with the national team. We've said that he'd cost €80million. At a pinch, I'd prefer to put down €20m more and buy Havertz to be happy.
"With Havertz, it's the guarantee of a playmaker that you could play with Lewandowski without a problem. [Thomas] Muller won't last forever."
Former Bayern president Uli Hoeness said on Saturday he hoped the club could sign Havertz as well as Sane, but he cast doubt on whether financial realities would allow for that.