Former Manchester United full-back Rafael believes Romelu Lukaku has the potential to be an exceptional player for Jose Mourinho's side.
United finalised a reported £75million deal for Lukaku on July 10 and the 24-year-old has enjoyed an encouraging pre-season, scoring against Real Salt Lake, Manchester City and Valerenga.
Rafael, who won three Premier League titles in a successful seven-year spell at Old Trafford, recalls Lukaku scoring a hat-trick for West Brom in a 5-5 draw with United in 2013 in Alex Ferguson's final game in charge of the club.
And the 27-year-old Lyon defender thinks Lukaku will prove to be an "excellent signing" for his old club if he can build on the performances he has shown in England's top flight.
"I've seen Lukaku play at Everton and a bit at Chelsea," he told Omnisport. "I saw him also when we were champions, and he was in West Brom, [which was] maybe my best time in Manchester.
"For me, he is a good player and is at a good age, an age he can evolve, but if he keeps what he did last year and in the last two or three years, he will be an excellent signing."
Rafael saw Lyon team-mate Alexandre Lacazette swap Ligue 1 for the Premier League this month when the France international sealed a reported €53m switch to Arsenal.
Former Gunners star Robert Pires has suggested Lacazette will need time to adapt to English football but Rafael does not expect that process to take long.
"I admired and still admire his football a lot," said the Brazilian. "He is a very smart player, he knows how to score. He's fast, and that's all an attacker needs. I think he will do very well at Arsenal.
"I guess so [he'll need to adapt] and I think it will not take that long. In the early games, he could struggle a little, but it will be fast."