Cheltenham Town keeper Carson kept three clean sheets in five games for the unbeaten Robins in August, including a late stop that preserved a 1-0 win at Bury on the opening day and an assist for the winning goal against Accrington Stanley a week later.
Four goals in five games sees Morecambe's veteran forward Ellison nominated. Two of the 35-year-old's strikes were free kicks and his performances helped the Shrimps to four wins in a row to start the season.
Lastly, AFC Wimbledon striker Tubbs also has four goals like Ellison, netting in all but one of the Dons' five games.
The winner will be announced on Friday.