The Japan right-back has missed 11 games with a calf injury.
On Tomiyasu, he stated: "Tomi is very, very close.
"Whether this game is going to be too early for him or not, again we will decide it today after the training session."
The Gunners will look to end a three-game losing streak against Thomas Tuchel's side.
Alexandre Lacazette is also recovering from Covid-19, but could return against the Blues.
"With Laca we are assessing him today to see if he is available with the team," he said.
"Obviously as you all know he had Covid so he's been away for a few days. So we're trying to get [how] he's feeling and where he's at if he can contribute somehow with the team."