The Hornets have been decimated by injuries over recent weeks, with 11 first-team players currently on the treatment table, and their problems have also coincided with a run of five Premier League games without a win.
Mazzarri is hopeful of welcoming some of his injured players back against Middlesbrough at Vicarage Road, with forward Okaka, who has been sidelined with a hamstring problem, set to feature for the first time since scoring a brace against Everton last month.
Full-back Janmaat is also closing on a comeback after injuring his leg during the Boxing Day draw with Crystal Palace while midfielder Behrami did play the opening 45 minutes of the recent defeat to Stoke and should now be fit enough to play a more prominent role following a hamstring complaint.
Mazzarri is pleased with the trio’s progress and is hopeful of having a fully-fit squad sooner rather than later.
The Italian said: “Yes, I think Okaka is already back training with the team but of course needs more intensity in the training but should be back. It’s very similar with Janmaat and Behrami.
"They should be ok and I have very high hopes that step by step very soon we will have the full squad again available."