I really don't think so. I'm not sure how you coach that header against Man U out of him. Earlier in the season, in the Saudi Sportswashing Machine game and I think one other game, he looked petrified under the high ball. Yesterday, he was weak and naive on the second and third goals. His distribution is also League One standard. He had the ball under no pressure at one stage yesterday in the first half and hit it straight to them which put us in all sorts of trouble because our players were on the front foot expecting to attack. Against Arsenal earlier in the season (admittedly at right back) he delivered arguably the worst defensive performance I've seen since his brickshow at Anfield in the 2-2 a couple of seasons back. On his day, he is very good but there are too few of those days and he has too many fundamental flaws to ever be the centre back we wanted him to be. He's not good enough.
I've highlighted specific instances above but they are symptomatic of a bigger problem with Sanchez and there are countless more examples. I heard a co-commentator say "he looks like he's playing in someone else's boots". That's actually an apt description of his performances in most games at the moment.
The first goal yesterday was just diabolical in terms of the lack of a screen in front of the back 4. Their man had an acre of space under no pressure in a position where I'd expect Sissoko or GLC to be. Sissoko was at right back (not sure if it was necessarily his fault because I couldn't watch it back without losing my brick). True, our defenders stood on the six yard line instead of pressing the ball when it ended up in our box but I couldn't believe what I was seeing from our midfield.