The 36-year-old halfback is looking at missing one to three weeks, but the Broncos are hoping he will recover in time for the round 26 home clash against Melbourne in a fortnight.
Reynolds had previously injured his left calf, but on this occasion he sustained what the club said was a soleus strain on his right calf after stretching out on Wednesday.
If the 323-game veteran half wasn't a week-to-week proposition previously, that is certainly the case now.
If Reynolds does not play again he will be remembered as a legend of the game who won two premierships, the first at South Sydney in 2014 and the second with the Broncos in 2025.
He turned the club around when he arrived in 2022 and took the side to the 2023 grand final.
This season has been a disaster for the 16th-placed Broncos, and for Reynolds it has been one of frustration since injuring a calf in round 15 and having a five-week layoff.
Three games into his return he was concussed early in the round 22 loss to Newcastle.
Ruled out of the round 23 clash with the Dolphins, he was then left out of Saturday night's home clash with the Warriors.
There has been confusion and conjecture about Reynolds' fitness this week, and AAP has been told that the two-time premiership winner can be feeling right one minute and then be in questionable shape the next.
Broncos coach Michael Maguire said he was not selected against the Warriors due to a calf complaint.
Maguire told News Corp that Reynolds was unable to train on Tuesday.
"He just can't," Maguire said.
"He has some issues with his calves and nerves and it's just bothering him. He has a neural issue with his calf."
Reynolds attended a function on Tuesday night and was asked why he was not named this week.
"Nothing really," he replied.
"It is a good opportunity for some young fellas to get a go and build on some combinations for the future."
Reynolds was then asked if his absence was "injury-related".
"No. I feel all right. I feel good," he said.
Reynolds' assertion of good health initially proved true on Wednesday when he trained with the main squad at Suncorp Stadium.
The Broncos published a short video of training on social media, and one of the eye-catching aspects of it was Reynolds running at full pace and appearing to be in fine fettle.
Some time after that vision was captured, Reynolds suffered another calf injury and scans revealed the damage.
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