Javi Garcia.
Played 80 games across two seasons for a team that finished 2nd & 1st in the Premier League, reached the FA Cup final, won the League Cup, and made it into the knockout stages of the Champions League. Forced Fernandinho out of the team during the 13-14 title-winning run-in and deputised admirably at centre-back on more than one occasion when other players had been sent off.
Yet some of our fans would have you believe he wasn't good enough to get a game for most relegated sides. A good player who was treated too harshly and was subsequently sold too early.
It took ages to properly replace him as well. After we sold Javi, we went out and bought Fernando. That didn't work so we bought Delph as well. That didn't work either so we tried out Aleix Garcia. We wasted three seasons trying to find someone as good as Javi and ended up forcing Yaya to play more often and for far longer than he should have done. Pep finally rectified the issue by changing to a midfield triangle.