Centre-back Greer was sent off in the second half of the club's dramatic semi-final second-leg penalty shoot-out victory over Charlton and is suspended for the showpiece finale to the season and the start of next term.
His replacement and a possible defensive reshuffle will depend on the fitness of on-loan left-back Alan Sheehan, who missed the encounter with a pelvic/groin injury and will be given as long as possible to prove his fitness.
But the Robins were boosted by Lucas' return to full training at the start of this week after he was forced off just five minutes in at The Valley having landed awkwardly and injured his shoulder. Lucas will again start between the sticks.
Leading scorer Billy Paynter has also been training this week after the hamstring injury that ruled him out of the first leg of the semi-final and he should be okay, while fellow forward Vincent Pericard has fully overcome his heel problem.