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The five-time Ballon d'Or winner completed a sensational return to Old Trafford two weeks ago for an initial fee of £12.9 million ($24.1 million)) on a two-year deal with the option of a third.

After being granted permission to leave Portugal duty early and then serving a period of isolation, Ronaldo reported to United's training ground for the first time on Wednesday (AEST).

He started training with his new team-mates on Thursday (AEST) and is now set to play his first Premier League game since May 2009 – the longest gap between appearances in the competition's history – this weekend.

"He had a good pre-season with Juventus, he's played for his national team and has had a good week with us here," Solskjaer said.

"He will definitely be on the pitch at some point, that's for sure."

Ronaldo scored 188 goals in 292 games in his first spell at United, which lasted for six years before he joined Real Madrid in 2009.

Despite that prolific return in front of goal, the Portugal captain scored just one hat-trick across that previous stint – against Sunday's (AEST) opponent Newcastle in January 2008.

Solskjaer expects the former Juventus man's return to also help get the most out of others in the squad as United looks to build on a return of two wins and a draw from its opening three Premier League games.

"Everyone is very happy to have him back. He can speak for himself but he seems happy to be back as well," Solskjaer said. 

"The mood has been good and we're looking forward to Saturday [Sunday AEST].

"The way he has come in and conducted himself... we know what he's achieved in his career but he's coming here to achieve more.

"He's lived the life of a top professional ever since he came here. You can't go into training and give 95 per cent and not be focused, that's what he demands from everyone."

Ronaldo has remained prolific across nine years with Real Madrid and three with Juventus, scoring a combined 551 goals in 572 matches in all competitions.

Asked what he is expecting from a player that finished top of the Serie A scoring charts in his last season with Juve, Solskjaer said: "Everyone evolves and develops throughout their career.

"Cristiano is a different player to the one who left but he's in such good nick still and will be looking in next few years to play and score as many goals as he can but also to be on the end of crosses and he's added something extra.

"We don't have his skill set in the team, the mix, no one has really. He is one of the best players that's ever played the game.

"He has developed, he has evolved as age goes by you have to change your game a little bit. You won't see those 18, 19, 20 stepovers before he goes past you.

"He has developed into one of the most accurate finishers. What he has developed on at Real Madrid has impressed us all. He is one of the best in the air, he still hits the target 99 out of 100 times when he shoots from outside the box as well. 

"He knows the game more, the positions and he is still as quick as he was it looks like, from the stats. Everyone is going to look up to him and he is going to be a leader in this dressing room."