According to TYC Sports (translated by Sportwitness), the Hammers submitted a bid for the player but it has been rejected.
Apparently, West Ham want to sign the player on loan for the remainder of this season and they want an option to sign him permanently in the summer.
The initial offer was of a €500,000 loan fee with a purchase option of €10m.
It will be interesting to see if West Ham come back with an improved offer for the player in the next few days. Montiel is highly rated in Argentina and the 23-year-old has managed to force his way into the national team setup as well.