Chaaban grabbed the only goal of the game to knock out Shrewsbury in the last round and wasted a glorious first-half chance against the League One Lions at Wheatsheaf Park on Saturday.
But after Paul Robinson's second-half header put Millwall ahead, Chaaban converted from the penalty spot to keep the Blue Square South side's dreams alive.
Staines almost took the lead in the 15th minute when Richard Butler slipped the ball through goalkeeper David Forde's legs only for Robinson to hook it clear.
Chaaban squandered the best chance of the first half in the 25th minute when he raced clear from midfield only to fire straight at Forde.
Millwall upped the tempo in the second half and in the 69th minute Staines cracked when Lions skipper Robinson rose highest from a corner to power his side ahead.
But Staines refused to throw in the towel and drew level in the 78th minute when Chaaban converted from the spot after Darren Ward brought down Butler.