Timber has recovered from an ACL injury and Arteta says he's completed all tests in training ahead of taking the next step.
Arteta said: "He still has a few steps to make and he will have a game to play with the Under-23s.
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"He has done everything in training."
On the title race, the manager added: "I think it's the motivation. They are super excited about what we are doing and the way the team is performing - they want more.
"We know the challenge ahead of us and how good we have to be to win it, but we are going to try."