Real Madrid and Spain legend Casillas suffered a heart attack in a training session in May 2019 and has since retired as a player.
Porto wrapped up the Primeira Liga title with two games to spare by beating Sporting CP 2-0 on Wednesday.
Supporters subsequently posted '#IkerCampeao' on social media in a bid to get the 39-year-old goalkeeper an appearance before the conclusion of the season so he can be part of the triumph.
15 meses después volví a pisar Dragão. Magníficos recuerdos! Emocionado por este Campeonato conquistado por @FCPorto! Enhorabuena a los los compañeros, al cuerpo técnico, al club y a los aficionados! PARABÉNS! 🔵⚪🏆🥇 pic.twitter.com/zSsWesb7Hk— Iker Casillas (@IkerCasillas) July 16, 2020
However, Conceicao criticized the movement because Casillas is not eligible to play for Porto anymore.
"People who ask for this have no idea what is going on. Iker cannot play," Conceicao said ahead of their meeting with Moreirense on Monday.
"I don't think he has medical authorization and he has no contract with Porto, it is finished. That has nothing to do with it. We could make a contract for a day or a month, but he has to be in a healthy state. It is not possible.
"People are poorly informed and then they create these movements… People have the right to write what they want, but then such movements emerge."
Porto president Jorge Nuno Pinto da Costa said Casillas had retired from playing upon him launching a bid to become the president of the Royal Spanish Football Federation in February.
Casillas pulled out of the running in May but has been linked with a return to Madrid as an advisor to club president Florentino Perez.
Conceicao said: "Iker was a super important player for all of us. If his return to Real Madrid is confirmed, he is in good health and has a lot of strength for this new project."