SANTA CLARA If the 49ers were worried about A.J. Jenkins entering Friday's game in Kansas City, his performance against Sean Smith, one of the league's biggest, most physical cornerbacks, triple underscored those doubts with a bright red marker.
Jenkins could not get off the line of scrimmage, could not get separation, could not get a catch. Two passes went in Jenkins' direction. Smith knocked one away and intercepted the other.
The 49ers don't play the Chiefs this season. But they play the Seahawks and their ultra-aggressive cornerbacks twice and the Rams and their pugnacious cornerback, Cortland Finnegan, twice.
Jenkins is fast and fluid, and he's only 23 years old. But for all of his potential, he's not strong, physical or feisty enough to be a factor for the 49ers this year, particularly in the rough-and-tumble NFC West.
The 49ers knew this when they drafted Jenkins 30th overall in 2012; general manager Trent Baalke said on draft day that Jenkins would need to get bigger and stronger.
More than anything, what prompted the 49ers to cut ties with Jenkins trading him to the Chiefs on Monday for wide receiver Jon Baldwin is that he never put in the work to improve his shortcomings.
Jenkins is marginally bigger than he was a year ago, but he wasn't part of the group of 49ers who show up every day at 6 a.m. to hit the weight room.
He's marginally more confident, but he still was knocked to the ground too often sometimes by phantom contact during practices, and he had as many drops in those sessions as big catches.
When quarterback Colin Kaepernick invited Jenkins to work out with him in Atlanta in February, Jenkins accepted but he showed up 12 days after Kaepernick and others.
Jim Harbaugh's mantra is, "Attack each day with an enthusiasm unknown to mankind." Jenkins' response seemed to be, "OK, coach, but is it OK if I start attacking at 11 a.m.?"
At team headquarters Monday, there were the usual platitudes wishing Jenkins the best, insisting he is a promising player and hoping he succeeds in Kansas City.
The player who came closest to hitting the truth about why Jenkins fizzled after just one season was tight end Vernon Davis, who has been one of Jenkins' most vocal defenders.
When asked what he'd tell Jenkins to do differently in Kansas City, Davis said: "Maybe take his approach toward the game up a notch. That can be something he can benefit from. Go above and beyond being a professional."
Davis stays after practice every day to catch passes from the JUGs machine; Jenkins never joined him.
In Baldwin, the 49ers get another wide receiver who has underachieved and lacks confidence. He was selected four spots higher No. 26 overall in the 2011 draft than Jenkins was in 2012. Baldwin was targeted three times Friday and, like Jenkins, made no catches, including a blatant drop of a pass from Alex Smith.
"I can tell you that when given the opportunity in this league, you'd better catch the football," Chiefs coach Andy Reid said after the game, foreshadowing things to come.
But Baldwin also has started 10 games in his two years; Jenkins has never started. Baldwin has 41 receptions and two touchdowns; Jenkins had only one pass go his way last season, and he dropped it.
Baldwin played in a very bad Chiefs offense last year, but he averaged 16.3 yards a catch, better than every 49ers wide receiver in 2012.
Most notably, Baldwin is 6-foot-4 and weighs 230 pounds. He may never turn into a starting wideout for the 49ers, but at least he'll be able to stay on his feet.