Free agent Caceres, 29, has been without a club since his contract at Juventus expired last June and is set to be drafted in at San Siro to alleviate Montella's injury concerns at full-back.
Luca Antonelli, Mattia De Sciglio and Davide Calabria are all sidelined, with the Milan boss forced to consider using Alessandro Romagnoli in an unfamiliar position on the left-hand side of the back four.
With his options restricted, Montella would welcome the addition of experienced Uruguay international Caceres – a five-time Scudetto winner during his time in Turin.
"I don't know a lot about the negotiation with Caceres. He's fit and could be of great help," said Montella ahead of Sunday's meeting with Sampdoria.
"[Leonel] Vangioni is coming on gradually. He has offensive qualities. He hasn't played for a while, I'll have to think carefully. Another option would be Romagnoli at left-back."
It is not just the defence that is giving Montella cause for concern, with Carlos Bacca struggling to replicate the impressive goalscoring form he showed in his debut season at San Siro.
The Milan boss feels more needs to be done to get the best out of the Colombia international, but called on Suso as well as new signings Gerard Deulofeu and Lucas Ocampos to prove their worth.
"Bacca is one of the strongest and most important players we have. He's 30 and at that age it's unlikely he'll change the way he plays. We have do adapt to his qualities and make the most of them," said Montella.
"I expect a lot from the strikers. Suso and Deulofeu have to be more clinical. We are competitive and we have shown it.
"We signed two great players who will have to improve and finally blossom. Gerard gives his best in tight space, while Ocampos does better with more space available."