From the Bolton forum
"Sorry that it didn't work out for Santos. Think he became the lightning rod for Evatt's tippy tappy. Over the years, a decent player for us."
"Santos had three good years here. Last two I think a bit questionable but three good years. And achieved a lot. He was overrated criminally by the last manager and some fans but that is not his fault. It’s a shame I think in some respects he never really had a proper manager because I do think he had the ability to get better and who knows - raw ability all there - big, quick and strong. The stuff you can’t teach he was good at. The stuff you can teach and learn sadly he never got good enough at - and I blame Evatt and his staff for that. Had a warnock or Allardyce or Pulis got hold of him - managers who know how to defend - I think he could have gone a lot further."
So he's good at old fashioned defending (in L1 and L2) but not a bring it out defender.