"He didn't have an ideal season last season, which was when he really needed to step up," Harris said yesterday. "But Blyth is an amazing athlete, so we're certainly not ruling him out.
"Santos has done [a highest category] 4-star before with his previous rider, so it's a bit about the combination starting to gel."
Five riders appear to have the whip hand on Olympic selection, providing form and fitness holds good - double Olympic champion Mark Todd, six-time Games veteran Andrew Nicholson, Jonathan Paget, Clarke Johnstone and Caroline Powell.
Powell is in a dilemma with getting clearance to ride Lenamore - her best horse - at the Games, from the horse's owners.
However she has two others who have qualified - Boston Two Tips and Porthall Rusty Nail.
The riders have a busy campaign leading up to the Games team naming. There are three key events on successive weekends; at Belton in Lincolnshire at the end of March; Burnham Market in Norfolk (both 3-star); and Weston Park, an advanced course just north of Wolverhampton.
The final hit-out for the New Zealanders will be at Barbury Castle in Wiltshire at the end of June, and will be significant if there are two or more combinations separated by little.
However Harris is confident a clear picture will have emerged after Badminton in May.