Devereux, 27, was jailed on Wednesday when a jury at Kingston Crown Court found him guilty of inflicting grievous bodily harm with intent on Rosslyn Park's Jamie Cowie in an on-field incident last February.
The court had heard that Devereux lashed out after the referee blew his whistle for a penalty after a ruck, with Cowie suffering a broken jaw in three places.
In a statement yesterday, the Gloucester club said: "While not in any way condoning violence, either on or off the rugby field, the club are shocked and dismayed by what they feel is a sentence by the court that is totally disproportionate to the offence. Until this event at Roslyn Park, Simon had an exemplary rugby career.
"The club has talked to Simon's legal advisors and we understand an early appeal will be made. In the meantime, the club will continue to support Simon and his family in those areas in which they require help. As the appeal process is about to start, the club now feels it will be imprudent to make any further comment as we would not wish to prejudice his appeal."
The court heard that Cowie's face "caved in" from the punch and the crack of his jaw breaking could be heard around the ground. He spent five nights in hospital and was unable to play for eight months.