The first leg ended 1-1 in Spain last week.
Chelsea’s impressive defensive record under Tuchel will be put to the test in the return leg.
But their hopes of breaking down Real’s defence could even be tougher, should Ramos return for the first time since March 13.
The 35-year-old suffered a calf injury playing for Spain and is working his way back to match fitness.
Tuchel however expects Ramos to start for the first time in nearly six weeks for his club.
He said: “Does Ramos play or not? This is a tough question because I simply don’t know it. We will see after the training today and when they give the line-up tomorrow.
“Does it change for Real Madrid? Yes, a lot. It’s the captain, it’s the captain of the most successful team in Europe in the last years, it changes a lot.
“We cannot lose our heads about this decision. I think he will start we will prepare for that and we have to make sure he cannot do it alone.