Hendrie, 57, played a key role when Barnsley upset the odds to reach the top flight under manager Danny Wilson for the only time in their history 24 years ago.
The Reds, now with Valerien Ismael in charge, secured an unlikely Championship play-off place last weekend and Hendrie will not be betting against them going all the way.
“They’re big outsiders,” said Hendrie. “But they’ve nothing to lose here. They’re getting a free hit because there’s no expectation.”
Barnsley survived relegation on the final day last season by winning at promotion-chasing Brentford and were among the favourites for the drop this time.
Odds of 500-1 were available in September for Barnsley to finish in the top six.
“It would be massive,” said Hendrie. “They’d probably give Ismael manager of the year for it. Promotion would be remarkable. Even just getting to the play-offs is a fantastic achievement.
“The odds are stacked against them, but it’s cup football and anything can happen.”
Barnsley had registered just four points from their first seven league games when former Crystal Palace defender Ismael replaced Gerhard Struber in October.
But former LASK chief Ismael, 45, steered them to 10 wins in their next 15 league matches.
“I’ve been as surprised as everyone else, I mean they were tipped for relegation but once they got some decent results, everything seemed to snowball. There are several factors obviously. Alex Mowatt has been inspirational, the new manager has done fabulously well and (Daryl) Dike has also been a big help.”
Dike has scored nine goals in 17 league appearances since arriving on loan from Orlando City, while another transfer-window signing, Carlton Morris, has chipped in with seven.
Hendrie feels Barnsley’s narrow FA Cup defeat to Chelsea in February was the springboard for a concerted play-off push.
“They probably gave Chelsea more problems than a lot of Premier League teams this season.
“I know Chelsea won 1-0, but Barnsley were excellent that day and on the back of that they kicked on, I think they won their next seven and went 10 league games unbeaten.”
When asked if promotion would top the class of 97’s achievement, Hendrie added: “I think it would be on a par.
“We went up automatically, but it’s probably harder to go up now. What we both had in common was that we both went under the radar.”
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