Rovers crumbled to their sixth defeat by four or more goals this season at Cheltenham Town on Saturday.
The 4-0 reverse left Gary McSheffrey's side four points adrift of safety in League One with games now starting to run out.
Ryan, 71, took to social media just moments after the final whistle at the Jonny-Rocks Stadium to voice his anguish at Rovers’ predicament.
“Utterly heartbreaking to see Rovers fall so far,” he wrote. “The display today wasn't even Conference standard.”
A red card for midfielder Adam Clayton for two bookable offences shortly after the restart rubbed salt into Rovers’ wounds.
And Ryan, often a critic of referees during his Rovers reign, could not resist labelling the performance of match official Peter Wright as "absolutely shocking".
Ryan was chairman of Rovers from 1998 to 2013, including a golden period in the club’s history which saw them promoted from the Conference to the Championship in the space of five years.
The club returned to the second tier for the first time in 50 years in 2008 and spent four seasons in the Championship before being relegated in 2012 following the failed ‘Experiment’ with agent Willie McKay.
Ryan encouraged Rovers fans to get behind rookie boss McSheffrey following his permanent appointment in December and remained upbeat about the club’s survival chances.
“Give Gary McSheffrey a chance,” Ryan posted on his Facebook page.
"He may well turn out to be a shrewd investment, he was a clever player and could be a young quality manager.
“When I appointed Sean O'Driscoll I was given a lot of abuse but look how that turned out.
“Gary needs some backing to bring in two or three quality players plus change a couple of loans.
“Get some injured players back and we could escape the drop and build again in the summer.”
Rovers remain 23rd in the table, four points from safety, and have played more games than all of their relegation rivals.
They have nine matches left to play and their next two fixtures are at home to Gillingham (22nd, currently one point better off) and away to Fleetwood Town (19th, currently four points better off).
Tomorrow’s fixtures: Crewe v Portsmouth, Plymouth Argyle v AFC Wimbledon, Sunderland v Fleetwood Town, Bolton Wanderers v Morecambe.