Time to worry about Christian McCaffrey?

SANTA CLARA – With fights popping off all around him Tuesday during the 49ers’ joint practice with the Titans, Christian McCaffrey stood off to the side, his nose buried in the offensive play sheet, watching it all unfold.For the second straight day, one of the best running backs in football, and the indisputable, irreplaceable engine of San Francisco’s offense, was held out of the action because of what the club is describing as “tightness.”No one has officially identified which McCaffrey limb, muscle, tendon or body part is barking.But if we’re keeping it a buck, it’s hard not to wonder whether the tightness is related to his calf.And if that sends a shiver down the spine of 49ers fans, there’s a pretty good reason for it.Two years ago, the calf tightness McCaffrey dealt with during training camp didn’t just carry over into the regular season.It hijacked the whole darn thing.What was initially described as a minor issue the 49ers and McCaffrey were managing out of precaution eventually became something far more serious.

The calf tightness developed into Achilles trouble and sidelined McCaffrey for the first eight games of the season.Upon returning in Week 9, he lasted just four games before suffering a PCL sprain.Season over.How did that turn out for the 49ers?Badly, to say the least.One year after playing in the Super Bowl, they slumped to 6-11.And if you think not having McCaffrey on the field didn’t play a significant role in that demise, you’re fooling yourself.McCaffrey wasn’t merely part of the 49ers’ Super Bowl run the season before.

He was the driving force behind it.California's top news, sports and entertainment delivered to your inbox every day.

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Never miss a story His 1,459 rushing yards led the NFL.He added 67 catches for 564 yards.

If you’re doing the math at home, tha...