Solskjaer told his strikers to be "more clinical" after needing a second-half penalty from Bruno Fernandes to see off relegation-threatened West Brom at Old Trafford on Saturday.
Greenwood was absent against Slaven Bilic's side following a lengthy illness but after returning to training, the Norwegian is hopeful of having the 19-year-old, who got 17 goals last season, available again soon.
"We're looking forward to having Mason back fit again and well, so hopefully we can hit some form like we did toward the end of last season," said Solskjaer.
"We need to improve. We need to get more flow and rhythm to our game, be more clinical and take our chances.
"We've got plenty of quality and sometimes the most difficult thing is to keep it simple and sometimes we want to over-complicate things. Yeah, we want players to seize opportunity but we need more flow, rhythm, make the opposition move."
Injury, illness and suspension have meant the trio have only started together twice so far this term but the United boss is hopeful his first-choice forward line can solve the problems in front of goal after managing just one goal from open play in five Premier League home games.
"I know the players have been away on international duty so hopefully now we'll have three or four months together," said Solskjaer.
"It's about sticking together, sticking to the way we want to play the game and improve every time.
"Defensively we're getting there, definitely; working hard, closing down, not conceding many chances. We need to be more clinical."