Greenwood is yet to score a competitive goal for United, but Solskjaer said he has seen enough during preseason and in training to believe that the 17-year-old is the best natural goalscorer at Old Trafford.
Asked whether Rashford or Martial is the most natural finisher in the squad, Solskjaer said: "They've still got a way to go, because Mason's more of a natural finisher than them."
Greenwood has been earmarked for a key role this season, following the departure of Romelu Lukaku.
The Belgium international's move to Inter Milan has also placed an extra goal-scoring burden on Rashford and Martial, and Solskjaer has told the pair the way to do it is by getting more "easy" goals.
"Anthony has had spells when he's played No.9 as a centre-forward under [Louis] Van Gaal, then he's played on the left the last few years," Solskjaer said.
"I think him and Marcus both are capable of playing both positions. Sometimes it will be Marcus through the middle and Anthony on the left, or Dan James on the left and maybe one of them on the right.
"But of course the goals are scored from between the posts and not the 'worldies' that we've seen them score -- both of them, Marcus and Anthony with curlers in the top corner.
"I want both of them to be scoring easy goals because you don't have to work too hard to score them, just a little bit of movement."