[5] On 1 February 2015, aged only 16, Villalba made his senior debut with Valencia's reserve team, coming on as a second-half substitute in a 1–2 away loss against CD Olímpic de Xàtiva in the Segunda División B championship.

[12] He made his debut three days later in the starting eleven for a 1–1 draw with Bristol City, came close to scoring from distance, and was the Birmingham Mail's man of the match.

[13] Although he did not readily adapt to the quicker, more physical style of the English game,[14][15] he was part of the starting eleven for the first four months of the season, apart from a spell out with a groin injury.

[16][17] He scored his first goal in a young Birmingham team that beat Middlesbrough 2–1 on 6 October – another shot was "somehow kept out ... at point blank range"[18] – but according to the Mail, "what earned him his 76th-minute standing ovation was the tireless pressing and harrying that characterised his second period.

"[19] However, with considerable competition in attacking midfield from Dan Crowley and new arrival Jérémie Bela as well as the emergence of the 16-year-old Jude Bellingham, Villalba dropped down the pecking order and out of the matchday squad.

[30] His first goal, from a shot that looped up off a defender and over the goalkeeper, opened the scoring in a 2–1 defeat of Leganés on 10 September that extended Sporting's unbeaten start to the season to five matches.

[32][33] Villalba's transfer to Sporting Gijón for an undisclosed fee was finally confirmed on 24 June 2022,[34] but on 16 August, he moved to Segunda División rivals Málaga on loan for the season.

[37] He found favour with new head coach Miguel Ángel Ramírez, and although an injury in pre-season prevented him establishing himself in the starting eleven, prompting suggestions of a possible departure on loan, although the player stated he wanted to stay.