The Red Devils were strongly linked with the 16-year-old in January, but the transfer window ultimately closed with the English youngster still at St Andrew's.
It is difficult to imagine the Blues keeping hold of the teenage talent this summer, though, and United appear to be ahead of the likes of Borussia Dortmund and Chelsea in the race.
Bellingham will not turn 17 until June but has been a regular for Birmingham this season, contributing four goals and three assists in 32 Championship appearances.
As a result, it would be fair to assume that he would immediately become part of United's first-team plans should he move to Old Trafford during this summer's transfer window.
Here, Sports Mole picks out five players in the Red Devils squad who could be affected by the youngster's arrival.
There is an argument that Bellingham would go straight above Lingard in the pecking order at Old Trafford should the youngster arrive this summer. Indeed, there is no getting away from the fact that it has been a tough season for Lingard, who has managed just two goals and two assists in 35 appearances in all competitions.
The England international's statistics in the Premier League are even more disappointing, failing to score or register an assist in 20 appearances, while he has not even been in the squad since the start of February.
Indeed, Bruno Fernandes's arrival has been bad news for Lingard, who has played just 23 minutes of Premier League football since featuring against Arsenal on New Year's Day.
The 27-year-old has a contract at Old Trafford until the summer of 2021 - with the option of an additional 12 months - but Bellingham's arrival could spell bad news for the academy product.
The 24-year-old has been used on 37 occasions by Ole Gunnar Solskjaer during the current season and his statistics are slightly better than Lingard's, contributing two goals and four assists in all competitions.
Pereira's numbers for an attacking midfielder are not at the required level, though, and he has also struggled for action over the last few weeks, failing to feature in any of his side's last three Premier League squads.
There is no question that the Brazilian has been given plenty of opportunities to contribute this season, but it has been a tough season for a player who has managed just four goals and five assists in 72 appearances for the 20-time English champions overall.
Like Lingard, Pereira has recently been linked with a move away from Old Trafford, and it is extremely difficult to see him securing regular football next season with Bellingham seemingly just one of a number of targets for the Red Devils.
Gomes, as it stands, will be out of contract at the end of the season, but United have allegedly offered the 19-year-old a new deal worth £30,000 a week.
The attacker has made six first-team appearances for the Red Devils this term although just two of those have come in the Premier League. There is little doubting his talent, but it remains to be seen whether he is given a serious opportunity to hold down a spot in the first team.
Gomes is in a similar situation to Lingard and Pereira in the sense that Bellingham's arrival would likely push him down the pecking order. The Birmingham youngster's ability to play in a number of different midfield and attacking positions makes him an even bigger attraction, and Gomes could ultimately turn down the chance to sign a new deal with the 20-time English champions in search of regular football elsewhere.
Mata's form has unquestionably improved since Fernandes arrived in January, and the 31-year-old has featured on a regular basis this season despite struggling for starts.
Indeed, the Spaniard has managed 31 appearances in all competitions, contributing three goals and five assists in the process. Mata's lack of pace and athleticism count against him when Solskjaer picks his team for the bigger matches, though, and it is difficult to see him receiving too much football next season.
There is an argument that Mata is the most technically gifted footballer in the United squad but much of the team's success under Solskjaer has been built on counter-attacking football, and Bellingham would surely also move above the former Valencia youngster in the pecking order should he arrive this summer.
Chong was strongly linked with a move away from United before signing a new contract earlier this month, extending his stay with the club until the end of the 2021-22 campaign.
The 20-year-old has made 11 appearances for the Red Devils this season, largely operating as a right winger.
Bellingham has played in central midfield, up front and on the left for Birmingham this season, but the majority of his football has come on the right, which would, in theory, make him a direct competitor for Chong.
It is worth reiterating that the Blues youngster only turned 16 last June, but it seems unlikely that United would pay potentially in excess of £30m for a player who would not be in the first-team picture next season.