Lukaku left United for Inter in a €65million deal in August and went on to score 17 Serie A goals before the season was halted by the coronavirus pandemic.
However, the former Chelsea and Everton striker could have instead been turning out for title rivals Juve this term.
Lukaku's agent Federico Pastorello claims Dybala's departure would have made room for the 26-year-old in Turin.
Dybala was linked with both United and Tottenham but instead stayed at Juve, netting seven times in the league so far in 2019-20 - including strikes in a pair of precious victories over Inter.
Pastorello told Sky Sport Italia: "If Lukaku is wearing the Inter shirt today, it's only because of Paulo Dybala's failure to join Manchester United."
However, Lukaku's representative also suggested the player felt a warmer welcome at Inter than he would have expected with Juve.
"Romelu wanted to leave the Premier League and move to a club where he felt loved," Pastorello said.
"He immediately noticed the affection and warmth of the Inter fans compared to those of Juve, and this made the difference.
"Lukaku's arrival at Juve would have pleased many fans, but for Inter his engagement instead represented a turning point after the arrival of Antonio Conte, the intention to try to start a winning cycle.
"He perceived this immediately, even on social media. He felt wanted at Inter. Conte put a lot of pressure on the club to have the player."