Yes, Cavani was out because of an injury for 6 months. He needed to train to reach a certain level of fitness so for us, starting him in all games it not always the answer.
I just don't think Ole has habit to throw a player just like that, especially when he comes from another league. It's not his way of doing things. He took 16 games to slot in Greenwood as a starter, and Cavani led the line against Istanbul in the CL so Greenwood was rotated in.
If Greenwood doesn't mess up his 2 chances, we score at least 2 goals in the first half, and the story of the game is slightly different.
If Martial is fit, then yes, I think Ole will try to rotate as much as possible. Cavani looking for the space behind tired opposition legs might actually be a good idea.