The France striker hit four goals in the 4-0 Champions League victory away in Sevilla on Wednesday before delivering the sobering message.
Giroud, 34, says the next month will be crucial for both his club and international hopes as he bids for more first-team action ahead of the Euros next summer.
He said: “I am ready to fight until the end. But obviously to be happy I need to be a little bit more on the pitch.
“I have a good chance to be ready for the Euros if I play more than in the beginning of the season.
“I had a conversation with France manager Didier Deschamps and he said if the situation stayed like that, you will have to make a decision in January.
"But I'm pretty sure I can grab more game-time and stay at Chelsea because that's what I want.
“But you never know in football — everything is going very fast."