Sparrow also faces missing a further three games - against Bradford, Yeovil and Northampton - after admitting an FA charge of violent conduct.
He clashed with Seagulls defender Adam El Abd as he left the Withdean Stadium pitch following his red card last week.
Iron manager Nigel Adkins must choose between Morris and on-loan Kevan Hurst to fill the left-wing spot vacated by Sparrow.
United are without new loan signing James Quinn, as the striker is on international duty with Northern Ireland.
Orient are without several key players - most notably their freescoring left-back Matt Lockwood.
He is out for a month after suffering an ankle injury against Oldham last weekend.
Donny Barnard, Michael Simpson and Efe Echanomi are all out through injuries, while striker Gary Alexander is ruled out through suspension.
But the London side welcome back defender Adam Chambers after a ban, while on-loan striker Gary Hooper is in line to make his first start for the club.