Cazorla hasn't featured for the team for 13 months since he picked up an achilles issue during their 6-0 Champions League win over Ludogorets.
The 32-year-old was initially expected to miss a few months but he's suffered a number of setbacks and was told by one doctor that he's lucky to be walking again.
He was told he could lose his foot after picking up an infection but is now on the road to recovery having undergone a last bout of reconstructive surgery on the injured tendon back in May.
Wenger said: "It is the worst injury I've known".
"It started with a pain in the achilles and it has gone from worse to worse and I must say I know how much Santi loves to play football and loves to be out there every day and I feel very sorry for what happened to him, because it is unbelievable". He has competent medical people around him and tries to practice.
Wenger said he also remains hopeful about a January return for the midfielder, but did not want to set any specific timeline.
I must admit, I have been dubious that I would ever see Cazorla back in the Arsenal colours, but going by what he and Wenger have said, we may yet get him back for the second half of the season.
Speaking earlier this month the Spanish worldwide said the infection had eaten the Achilles tendon on his right leg and that doctors feared the worst.
Arsenal, who are sixth in the league 12 points behind leaders Manchester City, host third-placed Tottenham Hotspur in a tightly-contested north London derby on Saturday.
Spain global Cazorla, who joined Arsenal from Malaga in 2012, recently told Spanish newspaper Marca he aims to be back playing in January.