Bill Romanowski Says He's Feeling Great Despite '20 Documented Concussions'

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Bill Romanowski tells TMZ Sports despite the repeated head trauma he suffered during his NFL career, he's still feeling great ... although he admits he has to work at it daily.

The legendary tough guy played linebacker for four different teams in the league from 1988 to 2003 ... and he revealed to us this week he ended up with "20 documented concussions" in that timeframe.

Bill Romanowski Getty

But, he said as of now, he's showing no signs of ill effects from the brain blows -- although he did relent he's working like a dog daily to make sure things stay that way.

"I got this saying," he told us, "'Don't let the old man in, because he's knocking every day.' I work…