[3] Onésimo's playing career began with his hometown club Real Valladolid, for whom he made nearly 50 first-team appearances before the age of 20.

[4] Onésimo's time at the Camp Nou was an unhappy one: Cruyff, who disapproved of the player's partying, selected him only twice in the league all season.

[5] Onésimo returned to Valladolid after a single season with Barcelona, and would experience both promotion and relegation with them the following years as well as with his next team, Rayo Vallecano.

[7] He left midway through the 2007–08 season to take charge of SD Huesca, whose manager, Manolo Villanova, had been appointed at Real Zaragoza.

[7] Even though he led the team to promotion from division three, Sánchez's contract was not renewed,[7] and he returned to Valladolid's reserves in 2009 following the dismissal of Paco de la Fuente.

[19] In June 2021, Sánchez added two more years to his contract as the team entered the new Primera Federación after a league restructuring,[20] but was dismissed halfway through.

[23] On 2 May 2024, after more than a year without a club, Sánchez was named manager of third division side UD Ibiza on a deal until the end of the season; he took over from Guillermo Fernández Romo.