McTominay has been United's best performer in midfield this season.
"He's finally nailed a position down for himself and played regularly," Solskjaer said ahead of their meeting with Sheffield United.
"He's played everywhere. He was a striker as a kid. He's learning the game now. His improvement has been great to see. We're going to miss him. Sheffield United, set plays, balls into the box, we'll miss Scott.
"If you take three out of any top club they'll struggle. It'll take it's toll, of course. Fred has stepped up.
"We have to conjure a way of replacing them. Long-term we're looking at different positions but we are looking at midfielders."