Barcelona announced earlier on Tuesday Puyol will undergo an arthroscopy on May 12 after feeling discomfort in his right knee after Saturday's 4-0 defeat of Espanyol with the approximate recuperation period around six weeks.
Del Bosque told AS: "It's a serious setback, he's a considerable loss not only for what he gives on the pitch, but for what he contributes to the team (off it)."
Puyol has won 99 caps since making his international debut in 2000 and was part of the Spain squad that won Euro 2008 and the 2010 World Cup.
Del Bosque added: "It's also a shame that this happened when he was on the verge of playing 100 caps, but hopefully he can get there. He was having a great end to the season."