Born in Madrid, Cuéllar represented Internacional de Argibay, DAV Santa Ana, CD Pegaso and AD San Federico as a youth.

As Osasuna "dropped" to the UEFA Cup Cuéllar, by then not an automatic first-choice in the league, played seven times in European competition, as the Navarrese reached the semifinals.

[8] Scottish club Rangers made two offers for Cuéllar in June 2007 that were rejected by Osasuna, but the eventual transfer was completed on 5 July, for a fee of £2.37 million.

[9] He signed a four-year contract, worth a reported £15,000 per week, and made his competitive Rangers debut against FK Zeta on 31 July 2007, in a 2–0 victory.

"[14] Following the departure of Thomas Buffel during the summer, Cuéllar was handed the number 4 shirt for the 2008–09 season, but never wore it as he was injured for the first game against Falkirk and transferred to Aston Villa just days later.

On 12 August 2008, English Premier League side Aston Villa signed Cuéllar in a deal worth £7.8 million on a four-year contract.

[17] Cuéllar made his official first team début on 18 September in the 3–1 UEFA Cup first round victory against PFC Litex Lovech in Bulgaria.

Most of Cuéllar's league appearances during his first season were in that position, due to the good form in the central partnership of Curtis Davies and Martin Laursen.

On 6 May 2012, following a 1–1 draw with Tottenham Hotspur that confirmed Aston Villa's Premier League survival, Cuéllar announced via his official Twitter and Facebook pages that he would leave the club at the end of his contract in the summer of 2012.

[30] Cuéllar was released by Norwich a few days after the club secured promotion back to the Premier League, having made 10 appearances for the Canaries.

On 10 August 2015, Cuéllar signed a one-year deal with UD Almería in the second level, mainly as a replacement to Levante UD-bound Ángel Trujillo.