The German joined the Super Lig giants on a free transfer from Bayern Munich in the summer but has endured a mixed start to his spell in Istanbul.
According to former Galatasaray defender, Sane’s sluggish start in Istanbul is largely due to his physical condition while comparing his situation to that of Hakim Ziyech.
"I think he wasn't fit enough and needs to get his head straight first," Erdem said in a Bild podcast.
"Gala have now won in the Champions League against Liverpool without Sane. He didn't even play for a minute, which says something.
“(Buruk) let Ziyech play five, six, seven, eight games and very quickly they let him go. It just didn't work out.
"I think Sane has underestimated that a little," Erdem continued.
"He may think he can get by at Gala without giving 100 per cent, but football isn't like that. No matter where you play, if you're not 100 per cent fit, it can happen very quickly and you're suddenly in the second division. He has to be careful there."