The Spaniards won 3-0 on Wednesday night to put one foot in the semi-finals, but Varane has warned that Real must be "solid" when they travel to Turkey for the second leg.
" We are content with our efforts but don't forget, we are only halfway through this tie," UEFA.com quotes Varane as saying.
"We will have to put in a solid performance away from home to seal qualification. Not letting a goal in tonight was important for us. We played well collectively and gave away very few spaces to their forwards.
"We want to win the Champions League this season but we must take things one step at a time."
The second leg takes place next Tuesday night.