He played the full 90 minutes but failed to break his duck in a Scotland shirt despite a couple of good openings.
The 24-year-old is yet to find the net for his country since making his debut in 2018.
Ferguson told Go Radio Football Show: "A lot of people look at Oli McBurnie coming in [as a reason for the defeat]. He's going through a tough time, but we've got to stick with him.
“I thought he worked hard enough, I thought he showed an appetite, he just needs that goal.
“We just need him to find the back of the net.
"I think when you make that number of changes it can work against you.
“I feel for him at times, I think a lot of the criticism is a joke if I'm being honest with you.
"We've heard him speak, and you could see what happened when he scored that penalty last week [against Serbia], there's a real passion in him and he works really hard."