Ronaldo, 36, is back at United after joining from Juventus at the end of the transfer window. He has trained since Tuesday and Solskjaer said he is fit enough to be involved at Old Trafford.
"He's been having a good preseason with Juventus, played with the national team, had a good week with us and he'll definitely be on the pitch at some point, that's for sure," Solskjaer told a news conference on Friday.
"We've followed his career from afar since he left here. Everyone is very, very happy to have him back. He seems happy to be back.
"The mood has been very good, working well and we're looking forward to Saturday."
There remains doubt about whether Fred will be eligible after Brazilian authorities invoked a FIFA rule to ban players from appearing from their clubs if they are not released to join up with their national team.
Fred and a number of other players were prevented by the Premier League from traveling to red-list countries during the international break.
"It's a lose-lose situation -- national teams, players and clubs -- it's been a farce, really," Solskjaer said.
"We're disappointed with the whole thing, common sense might not be common anymore. Fingers crossed, some sense comes into people's minds."