Denayer is expected to sign for the Lions shortly after according to Hürriyet.
The 20-year-old defender has been in talks with Galatasaray over a one-year loan move with a future buyout clause.
The Lions have made strengthening the defence a priority over the transfer window.
Galatasaray are however, facing competition from Ligue 1 giants Marseille for the young defenders signature.
Denayer scored six goals and provided two assists in 44 appearances for Scottish giants Celtic in all competitions last season.
The Istanbul giants would be able to offer Denayer Champions League football after winning the league title for a record 20th time.
Galatasaray booked a place in the Champions League group stages for the fourth consecutive season after lifting the 2014-15 title.