The Manchester Evening News says Mengi and goalkeeper Dean Henderson are in the squad to travel to Luton.
The United squad were pictured parking up at the Signature Private Terminal at Manchester Airport on Tuesday morning ahead of their their flight to Luton.
United travel to Kenilworth Road for their Carabao Cup clash against the Hatters tonight, which kicks off at 8.15pm. Ole Gunnar Solskjaer's squad are looking to bounce back from their opening Premier League defeat to Crystal Palace on Saturday.
Mengi and Henderson could be handed full debuts by Solskjaer, while the Norwegian is likely to include plenty of first team regulars to build his side's match fitness.
United squad members: Harry Maguire, Daniel James, Odion Ighalo, Dean Henderson, Bruno Fernandes, Jesse Lingard, Marcus Rashford, Mason Greenwood, Teden Mengi, Brandon Williams, Aaron Wan-Bissaka, Nemanja Matic, others unconfirmed.