The 22-year-old forward, who made his first-team debut for his boyhood club during the Magpies' FA Cup replay win over Rochdale in January 2020, headed to Cappielow in August but has returned to Tyneside after making 11 competitive appearances.
Allan was involved with Newcastle's senior squad in pre-season, making three substitute appearances against Doncaster Rovers, Burton Albion and Burnley before carrying out the second loan spell of his career.
The Ashington-born winger, who can also play as a striker, spent the first-half of the 2020/21 campaign on loan at League One side Accrington Stanley, making his Football League debut during his stint at the Wham Stadium.
Meanwhile, goalkeeper Jake Turner has returned from a loan spell at League Two outfit Colchester United.