As had been the case on the opening day at Royal Johannesburg and Kensington, the duo had matching scores. But their second-round one-under-par 69s left them two shots outside the cut mark after they'd left themselves too much ground to make up.
Drysdale, who finished third in this event 12 months ago, had six birdies in his second-day effort and will be hoping to maintain that form when he moves on to the Middle East for next week's Abu Dhabi Golf Championship.
Gallacher, who is the first reserve for that event and looks certain to get in, bagged four birdies in his 69 and, his putting apart, has been happy enough with his game on his return to the circuit.
He is also hopeful about playing in Qatar the week after Abu Dhabi and will be heading to India as well the week after the Dubai Desert Classic.
Jamie McLeary, who is attached to Marriott Dalmahoy, also missed the cut in Johannesburg after following his opening 68 with a 74.
But South African Charl Schwartzel shot a bogey-free 68 and has a real chance to record back-to-back wins following his victory at the Africa Open.
He went into today's third round on 11 under par – just one shot behind England's David Lynn. German Martin Kaymer was the last player to capture two successive events on the European Tour, beating Lee Westwood in a play-off for the French Open last July and then capturing the Scottish Open seven days later.
Schwartzel said: "It seems like the form from last week is carrying over and, with a good weekend, it could get very interesting."