Maybe "poor" was too harsh and I was judging too much on his more recent form - he only has 3 league goals in 2021. In the league this season his goals have been against Brighton, Newcastle, Sheff Utd, Wolves, West Ham, Leicester and Southampton. Assists are pretty similar reading.
For one of our "most important players" I would suggest that his record against the bigger sides has not been good enough this year.
Honestly the concern right now (without personally knowing Marcus or having any great insight into him) is if he has simply lost his love for the game, or has decided to switch his focus to off-field activities. He wouldnt be the first high profiler footballer to do so.