major obstacle
serious obstacle

He simply pointed out a major obstacle of which I knew nothing.

Until recently, two major obstacles have stood in the way.

The issue was expected to be the major obstacle to any agreement being reached.

But two major obstacles stand in the way: money and management.

Of course, there are some major obstacles in the way.

Fuel is a major obstacle, as running out of it results in game over.

The major obstacles to this are time, money and political will.

Lack of support from parents is often a major obstacle.

"And various times I considered him one of our major obstacles."

Especially the difficult supply situation was thought to be a major obstacle.