The 24-year-old was a noticeable absentee from the Blues squad that travelled to the Lamex Stadium fixture.
The summer arrival from Wigan had featured in all six games ahead of the Boro game, starting four of them.
But he didn’t make the trip to Hertfordshire as Mousinho handed a first league start to Jack Sparkes on the left wing and played Gavin Whyte in the no10 goal.
Pompey’s inability to break down their hosts and deliver decent service to centre-forward Colby Bishop was a feature of the goalless draw,
And after being asked why Scully wasn’t involved in a game lacking real attacking purpose, Mousinho revealed a knee injury – sustained during Tuesday night’s EFL Trophy game against Fulham under-21s – prevented the wide man from playing his part.
The result of a scan will help the Blues determine how serious the injury actually is.
‘Anthony Scully was just struggling with a knee injury and we’re not sure what that looks like yet,’ said Mousinho when asked about Scully.
‘Nothing serious, but he just went for a scan, I think on Friday, so we’re just waiting to see the result of that.’
Scully was one of three injured players ruled out of the trip to Stevenage, with midfielder Tom Lowery and forward Kusini Yengi also currently sidelined.
In midweek he scored from the penalty spot – after coming off the bench – as Pompey earned a penalty shoot-out bonus point following their 3-3 draw with the youngsters Cottagers in the Trophy.
With less than a week to go until the transfer window closes, Pompey are carefully weighing up their options but are expected to bring in another attack-minded player to bring their number of new recruits this summer to 14.
Scully is also likely to miss Tuesday night’s Carabao Cup game against Peterborough at Fratton Park.