Sir Alex Ferguson admitted Cluj had offered a stiff test to Manchester United after his side scraped a 2-1 victory in Romania.
Asked by ITV's Gabriel Clarke whether he felt his side had made hard work of beating Cluj, the United boss said: "If you see the way they kept going at the end - they put so many telling crosses into the box, which kept us under pressure all the time, kept us on edge."
And Ferguson also praised his own team, who won the tie through two Robin van Persie goals.
"I've got to be pleased that the concentration was good tonight," he said. "Apart from the goal we defended really well tonight."