The Manchester United manager argued that the Premier League is more challenging than other leading leagues, which means teams on the continent can afford to rest players throughout the season and keep them fresh for the closing stages of Europe's elite competition.
Toure was left out of City's squad for the trip to Rotterdam and, although he refused to be draw on specifics, Guardiola told a pre-match news conference the experienced midfielder "knows the reason why".
Despite City's £215m outlay on players this summer, Guardiola said he still sees a gulf of experience and confidence between his own side and the usual favourites, including his former clubs, Barcelona and Bayern Munich.
Guardiola did stress he is happy with Toure, saying: "I'm always happy, but of course I demand as much as possible from everyone".
He returned to watch the final stages of his side's victory, and City boss Guardiola said after the game he hoped Ederson "can come back soon". Feyenoord have more titles [they won the European Cup in 1970] than Manchester City. While they are without the injured Nicolai Jorgensen, who was the league's top scorer with 21 last season, Guardiola struck a cautious note.
Toure was an unused substitute for City's first three games of the season before being left out of the squad for Saturday's defeat of Liverpool. When asked about the Ivorian's absence from his side, the City manager said: "I spoke with him, he knows the reason why".
It is just a sporting decision, ' he said. That, in turn, led to a longer period of isolation.
However, the match at the De Kuip has come too soon for his captain, Vincent Kompany, who remains sidelined with a calf injury he suffered on worldwide duty with Belgium.
Starsport understands Guardiola has genuine concerns that Toure's legs have gone and that he isn't mobile enough to perform at the highest level. Six players finished their contract and he was the only one who stayed because he's a special player.
Goalkeeper Ederson faces a late fitness test after his collision with Sadio Mane during the 5-0 thrashing of Liverpool.
"But the decision why he hasn't played this season and is not in the squad - he knows the reason why".