Gerry Armstrong told Revista that relegated Villarreal have paid the price for failing to invest in their squad.
The Yellow Submarine, who played in this year's Champions League, were demoted to the Spanish second tier on Sunday following a 1-0 home loss to Atletico Madrid.
Armstrong says the absence of long-term knee-injury victim Giuseppe Rossi has significantly hindered Villarreal this season.
But he thinks the Valencia-based outfit would still be a La Liga club if they had tried harder to draft in new players.
"The big factor was not having Giuseppe Rossi," said Armstrong. "He would have contributed to 20 or 30 goals that would have kept them up.
"But that is not enough of an excuse and you have to have more strength in depth than that.
"You get what you put in and I don't think they have invested in the club enough in the last four years and they haven't developed. It is a shame."
Malaga, meanwhile, snared a Champions League berth on the final day of the campaign after Salomon Rondón's goal earned them a 1-0 win over Sporting Gijon.
The Andalusians were purchased by Qatari tycoon Sheikh Abdullah Al Thani in the summer of 2010, but have been relatively circumspect in the transfer market since then, with Jeremy Toulalan and Santi Cazorla two of the few big-money arrivals.
However, Graham Hunter thinks the La Rosaleda side must loosen the purse strings if they are to make an impression against Europe's elite clubs.
"They have said they don't want to [do a Man City]," said Hunter. "They've got similarly rich owners but they have said that they want steady growth and that they must not destroy the character of the club.
"They have got quality in Toulalan and Cazorla and Manuel Pellegrini is a super coach, but compared to Real Madrid and Barcelona they are too slow across the pitch.
"They need to adjust their philosophy; organic growth is fine but they need to buy quality and experience. How they invest will decide how close to the coattails of Man City they are."
Athletic Bilbao also enjoyed a prosperous campaign, claiming a top-half finish, reaching the final of the Europa League and earing rave reviews for their crisp, passing football, with striker Fernando Llorente and midfielders Markel Susaeta and Ander Herrera garnering particular acclaim.
Hunter believes Marcelo Bielsa's charges, who will contest the Copa del Rey final against Barcelona on Friday week, can make even greater strides next term - as long as their stars are not poached away.
"This is a golden generation of young Basques who are in the prime of their career and Marcelo Bielsa has added lion's claws to the young lions," he added.
"It is legitimate for them to aim for a trophy but to challenge regularly for the title this golden generation needs to spread by three or four more players - and to not have them pillaged in the transfer market."