The Frenchman claims that the England international forward was not fit to start in their Premier League encounter at the Emirates Stadium due to a stomach problem.
"Walcott couldn't practise before we played our last game at Cardiff [City] because he was sick," London24.com quotes him as saying.
"When we came back on Monday, he was sick again, so he just had a little session. In the last week he has not practised at all, so I was never tempted to start him.
"He has not played for seven weeks and he did very little in the last week. He is not completely ready."