The 24-year-old has been widely linked with Liverpool this summer, but the Ukrainian outfit are not prepared to entertain offers of less than £25m for the midfielder.
Palkin told Futbol: "I don't know where Mkhitaryan is now, solely his agent knows this. Borussia offered £19.5m for the midfielder. I contacted Mkhitaryan's agent yesterday. I wrote to him about the official position of the club.
"We are prepared to sell Mkhitaryan for £25m, this offer stands for the next 10 days. If Mkhitaryan wishes to leave, they have to pay this amount for him. If there is a club that can pay that amount, we are ready to make a deal."
Mkhitaryan scored 25 league goals for the club last season.