"It's been hard, of course," he told Arsenal's official matchday programme. "I lost most of pre-season because I was away with France [at Euro 2012], and then I had an injury right at the beginning of the season.
"It was difficult to come back from that quickly - the season had started, the players were up and running and you need time to get back to the required level.
"I know that I've played some good games and some not so good this season, but I'm working hard to stay fit and well."
Koscielny added that he is keen to improve himself amidst competition for places in central defence.
"We have great competition for places at the back with guys like Per, Thomas and Johan, and we have a lot of respect for each other," he said.
"It's healthy for us, and we don't stop trying to improve as individuals and as a unit."
Koscielny joined Arsenal from French club Lorient in 2010.