The midfielder, who has been with Osasuna for 17 years, made his final appearance in Sunday's 2-1 win over Real Betis.
Despite the victory, Osasuna were relegated into the Segunda after other results went against them.
"My career hasn't been easy, it's been rather difficult really, but I didn't know the hardest part would be left for the end," Inside Spanish Football quotes Punal as saying at a press conference.
"I'm very hurt and disappointed by how things have gone down, but other than that, I'm very happy to be from here, with how the people work, the people from here.
"There will be time to analyse what went wrong, but I'm very proud. It would've been a lot easier if I'd have had a sending off under better circumstances, not just for me but for the team. I think the fans were extraordinary. The players are crestfallen, I've never had to live through a relegation, but it's very, very hard."
Punal departs Osasuna having made 513 appearances.