The 25-year-old midfielder joined Luton Town in the summer of 2021 from Scottish top flight outfit Motherwell.
Campbell played a crucial role in helping the Hatters earn promotion to the Premier League last season, making 43 appearances in the league.
However, the midfielder has fallen down the pecking order in Rob Edwards’ side and has failed to make any appearances for Luton so far this season.
The Premier League outfit are open to letting Campbell leave this summer and he has interest from the Championship.
Bristol City and Millwall are rivalling each other to secure the services of the Luton Town star on deadline day.
Millwall have already brought in a host of players, but Gary Rowett believes that the Lions need to strengthen their midfield.
Bristol City have money in the bank after selling Alex Scott this summer and Nigel Pearson wants to bring in the experienced Campbell to bolster his midfield.
