Unzue was the number two to Luis Enrique in the Camp Nou hotseat for three seasons between the 2014-15 and 2016-17 seasons, winning two La Liga crowns, three Copa del Rey titles and the Champions League in their first campaign.
Unzue has explained in quotes carried by Marca: “What has kept Messi going has been his ambition and this brings a high level of stress.
“He demands himself to continue being the best and therefore, Messi demands the maximum from everyone, be they teammates, the physiotherapist or the coach.
“This produces a lot of stress and many cannot cope with the stress.”
The former goalkeeper had managerial stints at Numancia and Racing Santander and was then at the helm in the Celta dugout in the 2017-18 campaign before being appointed at Girona at the start of the current campaign but left after just 12 matches at the helm.
Unzue announced in June that he had been diagnosed with motor neurone disease – a debilitating disease that can lead to paralysis.