Dernard Span has recently become out of the question.
MLBTradeRumors has announced that in exchange for Dernard Span, the Twins want a MLB starting pitcher. I see no way no how the Reds will do this.
As of July 29th, the Reds have used the same 5 starting pitchers the entire season. The staff's starting pitchers claim 41 of the Reds 61 wins (an overall 41-26 record for starters.) 67% of the wins. Nothing is wrong with the Reds current rotation, and actually they are on a huge roll, the Reds winning 10 straight.
Leake has the worst record as a starter on the Reds roster, (4-6) but there is little to no chance Leake is a trade item. Bailey is the most likely out of the rotation to be traded, but I highly doubt it.
Span is not an essential, so I think the Reds just threw out all thoughts on acquiring Span.