25-year-old Strong missed the 2018 NFL season after suffering a torn ACL during his stint with the Jacksonville Jaguars ... but healed up and signed with the Browns in Feb. 2019.

Cleveland was expecting big things from the former Houston Texans 3rd round draft pick -- which is why many were surprised to see him get his walking papers during the preseason.

Now, Strong is sounding off about his time in Cleveland ... essentially accusing the team of ignoring his constant knee pain -- and working him so hard, his body nearly broke.

Strong is specifically pointing to the Browns preseason training regimen -- claiming the team ran an "unheard of" 30 straight padded practices ... which took a serious toll on the players.

"We played a full season in camp. The real season is here and they are already behind the 8 ball. Hamstring issues at DB? That’s just saying they’re being overworked!!!!"

As for Strong's case ... the WR claims team doctors knew his body was suffering from the intense camp -- "my knee swelled up day after day" -- but he was never offered a recovery day off.

"We get to week 3 of preseason and I can barely walk," Strong says ... "I was dead ... body legs etc."

The Browns ultimately cut Strong on August 27 after he performed poorly in a preseason game -- but notes, "the Browns knew why I looked and felt the way I felt after making play after play in camp for 30 straight padded practices."

The claims come days after Browns QB Baker Mayfield called out the Browns training staff for mishandling Odell Beckham's sports hernia injury, which he also suffered during the preseason.