Midfielder Mata played alongside Lukaku during their time at Chelsea and they are set to reunite at Old Trafford under their former boss, Jose Mourinho.
Lukaku is moving to United after a fee of £75million with add ons was agreed with Everton, report the Manchester Evening News.
The 24-year-old is expected to join up with his new teammates in Los Angeles for United’s pre-season tour of America and Mata has spoken positively about what he will bring to Old Trafford.
Speaking to Marca, Mata said: “We played together for Chelsea and he [Lukaku] has had a lot of good seasons at Everton.
“He knows the coach well, and scores a lot of goals which we hope he will carry on so we can try to win the league.”
Mata added he was already looking ahead to the Super Cup final against Real Madrid on August 8 – with former Real Madrid coach Mourinho also doing the same.
The Spain international explained: “I think Jose is already thinking about the final, and has been since Real won the Champions League.
The coach wants to win the trophy whilst in charge at United and although Zinedine Zidane had an incredible year in charge, we will try to create problems for them.”
Chelsea matched United’s bid for Lukaku on Friday but it is understood Lukaku’s agent Mino Raiola advised the Belgian to join United over his former club.
The Premier League champions have not confirmed their offer through their official website or social media channels and it is believed United are hopeful of concluding the Lukaku deal by the end of the weekend.
Senior United sources insist Lukaku was their ‘principal target’ they had pursued ‘for months’.
United have made an official announcement to underline their confidence in signing the goalscorer ahead of Chelsea.
The club wrote on Twitter: “MUFC is delighted to announce a fee has been agreed with Everton for the transfer of Romelu Lukaku, subject to a medical & personal terms.
“A further announcement will be made in due course.”