The 40-year-old keeper had been training with AFC Wimbledon to sustain his fitness after leaving Chelsea
Caballero, 40, – who had been training with AFC Wimbledon to sustain his fitness since leaving Chelsea in the summer – signed a short-term contract on Monday with Saints goalkeepers Alex McCarthy and Fraser Forster both sidelined by injury.
Harry Lewis was on the bench for last weekend’s 1-1 draw with Brighton, but the 23-year-old academy graduate has yet to make his Premier League debut.
“Alex is out for three to four weeks,” Hasenhuttl said ahead of Saturday’s trip to north London. “Fraser tried this week but it’s a little bit too early for him. That’s the reason we signed Willy and we’re happy to have him here.
“We’ve worked with him on some information, video clips, so he knows how he has to play with the ball and against the ball. It’s important for a goalkeeper.
“He’s a smart guy, he is fit and coming in with a willingness to help us and this is what we need now.”
Argentina international Caballero moved from Malaga to Manchester City in 2014 and spent three years at the Etihad Stadium.
He spent four years at Chelsea, adding only 38 appearances to the 48 he made in Manchester.
But Caballero is used to winning trophies with Champions League, Europa League, FA Cup and League Cup triumphs all on his CV.
Hasenhuttl said: “We were looking at a few options and he was the best for us.
“He’s experienced, he’s good on the ball, he knows out to play out from behind, how to stay high and defend behind a high defensive line in some moments.
“He is a good package for us and hopefully he is on the level on the weekend that we need against Arsenal.
“He is also a goalkeeper who makes some saves. We will try for them not to have many chances and hopefully it will be a good performance.”
Hasenhuttl, who will welcome back defender Jan Bednarek but has a fitness concern over striker Che Adams, insists Southampton are maintaining “very harsh” protocols to protect against the spread of coronavirus.
Tottenham’s Europa Conference League game with Rennes on Thursday was called off following a coronavirus outbreak at the London club, while Leicester will be without several players for their Europa League tie against Napoli because of Covid-19.
Hasenhuttl said: “We haven’t changed anything because I think our rules and restrictions are very harsh.
“They are definitely near the highest level since the beginning of the pandemic. Still not a lot of people in the building, we are still wearing masks and we are very careful about the social distancing in any room.
“We also have a very high vaccination rate, boostering, all things you have to do if you want to be aware and not to lose 13 people or more from the virus.”
Hasenhuttl added that other health and safety measures have been in place at the club, saying: “We had one situation where players went out for a dinner. We had a few issues with this dinner and we’ve tried to avoid these things for a long time.
“Also we had the behaviour of players meeting after a game with the families, which we stopped.
“It’s not possible at the moment. We have to be very careful of not getting any risk of losing a player with the virus.”