Burak Yilmaz opened the scoring in Istanbul, but a Jermaine Jones equaliser gave the Bundesliga side a valuable away goal on Wednesday night
After Burak Yilmuz opened the scoring, the home side had chances to go 2-0 up in an open and entertaining first half, but Jermaine Jones equalised in the 45th minute to ensure the tie remains in the balance ahead of the second leg.
"We created two great oppurtunities to make it 2-0, then the equaliser damaged our morale just before half time," Terim told reporters after the game.
"We went in front with a great goal, but after that made too many sloppy mistakes. We were not at our best and we know there will be no excuses in Germany."
Yilmaz's goal was his seventh of Gala's Champions League campaign and somewhat overshadowed Didier Drogba's return to the competition in the process.
He added: "I'm ecstatic with Burak's form, he keeps working and tries to improve."
The 59-year-old will hope the striker's scoring run continues when the two sides meet for the return fixture at the Veltins Arena on March 12.