Hart has been the undisputed number one at Celtic since joining the club in 2021 and has 92 appearances under his belt for the Scottish champions in all competitions.
He still has more than a year left on his contract and there are no signs that Ange Postecoglou is looking at anyone to replace the former England number-one between the sticks at Parkhead.
However, McManus insisted that Celtic can do better in the goalkeeper department next season.
He conceded that Hart is unlikely to face too many challenges in Scotland given Celtic completely dominate possession.
However, the former Scottish Premiership star believes in order to do better in the Champions League, Celtic need a better goalkeeper than the 35-year-old.
McManus took to Twitter and wrote: “The question was ‘How do Celtic compete better in the Champions League and what areas do they need to improve in?’
“Hart is a good goalkeeper but keeping clean sheets at Celtic domestically is expected as [they] dominate ball/games every week.
“Different story in the Champions League. Think Celtic can get better.”
It remains to be seen whether Postecoglou decides to bring in a goalkeeper to push Hart for a place in the starting eleven next season.