The Germans have thrashed out a deal with their Swiss counterparts for the 24-year-old winger, who will move to the Veltins Arena on a four-year contract for an initial fee of €5 million, which could rise to €8m depending on various add-ons included in the deal.
However, the proposed switch to Gelsenkirchen is dependent upon die Knappen's progression to the group stages of Europe's elite competition, which hangs in the balance after Jen Keller's men were held to a 1-1 draw at home to Greek outfit PAOK on Wednesday.
The Germans travel to Thessaloniki on Tuesday for the second leg and, if they secure their passage through to the Champions League proper, the Switzerland international will complete the move to the Veltins-Arena.
Stocker, whose contracts with the Swiss giants expires in 2016, has netted 58 times during his six-year spell with the club.
