Manchester United may be in the midst of a Cristiano Ronaldo love-in following his return, but pundit Graeme Souness insists the Red Devils will massively regret another of Ole Gunnar Solskjaer’s big transfer decisions.Ronaldo scored twice on a dream return to the United line-up as Newcastle were despatched 4-1. Amid a media-frenzy, the Portuguese superstar did not disappoint, despite the player admitting he surpassed his own expectations before the game.He wasn’t the only Premier League star though to net a double in front of his adoring home fans this weekend. Indeed, the feat was also matched by Odsonne Eduoard for Crystal Palace and Romelu Lukaku at Chelsea.Powerful Belgian Lukaku is back in the Premier League after a successful two-year spell at Inter Milan.The Blues broke their transfer record to secure his return, paying the Serie A champions £97.5m for his services.Lukaku looks hungry to prove a point to Premier League audiences after being shamelessy cast aside by Solskjaer at United.He moved the striker on for a fee of around £74m, deciding his style of play wasn’t what was needed at Old Trafford.However, he is now considered one of the best centre forwards in world football. And while they won’t admit it publicly, Souness reckons they’ll now reckon his sale was a major mistake.I dont think Manchester United shouldve ever let him go, Souness told Sky Sports.“He seemed unhappy when he was there, and hes come back a happy man.“He definitely is a key man. Goals change games. If you have someone who can nick goals then all of a sudden youre a different team.“He hasnt got a weakness. Im not saying hes brilliant at everything but hes got no obvious weakness.“If youre playing against him and youre a centre-back youre not going to enjoy it.“I dont think anyone will enjoy playing against him. Hes got a bit of everything in his game and hell be the difference for them should he stay fit.”Cristiano Ronaldo’s 10 most iconic club moments for Manchester United, Real Madrid and JuventusLukaku seems far happier since switching to first and Inter and now Chelsea. Both sides play to his strengths, which was altogether different at United, who often deployed him out wide.“I first learned to speak Italian whilst watching my brother Jordan playing for Lazio on TV,” Lukaku told Corriere Dello Sport.“Once I learned that [Ole Gunnar] Solsjkaer planned to put me on the wing, then I knew my time at Manchester United was over.“One bad year can happen to everybody in their career.“It was just done for me. You know what happened behind the scenes, it was just done. For me, it was done.“It was a difficult situation where for myself I had to make a decision where I have to go somewhere where I can learn other aspects of my game and work with somebody that wanted me as well.“Ole wanted me to stay, but I told him I was over. I didn’t have the energy. All credit to him because he’s been a man and he helped me make the move away.”READ MORE: Man Utd move hints at exit with forgotten mans return boosting transfer chances