Colorado Rockies outfielder Carlos Gonzalez underwent season-ending knee surgery in 2014 after suffering a left patella tendon injury. It could still be a problem heading into the 2015 season.

According to Nick Groke of The Denver Post, the 29-year-old exited Friday's game against the San Diego Padres with a sore left knee. Gonzalez chased down a fly ball hit off the bat of Will Middlebrooks in the third inning and seemingly aggravated the recovering injury.

"When you start putting a lot of pressure on your knees and your legs, you're going to feel a little pain here or there," Gonzalez told AJ Cassavell of MLB.com. "I don't think it's something major. Just a little fatigue."

The All-Star outfielder was ahead of schedule in his rehab and made his spring debut earlier than expected, but this is something to be concerned with, especially considering his well-documented injury troubles. Gonzalez hasn't played in more than 135 games since 2010 and has only 180 under his belt over the past two seasons.

Although he has played well in 11 games this spring (.333/.399/.444 with two runs scored and three RBIs), a setback with his surgically repaired knee could significantly hamper his ability to participate this season. It will also likely affect his trade value, which is notable since new general manager Jeff Bridich said he would listen to trade offers for the outfielder earlier in the offseason. It was said the Rockies would really only consider trading Gonzalez and/or shortstop Troy Tulowitzki if they could get full value in return.

His surgery was nothing to overlook. He had a torn portion of his tendon cut out, a bursa sack removed and a "fat pad" cleaned up. Due to the various procedures conducted, his recovery time was largely a mystery at first, and apparently could still be since he's already experiencing soreness. Gonzalez will be using his knees an awful lot chasing down balls in the outfield, so the Rockies may opt to err on the side of caution.

Today he told reporters he was "pain free," but he was kept out of the starting lineup because of head athletic trainer Keith Duggar.

''I checked with the doctor and he said, of course, there are going to be some days when I don't feel great,'' Gonzalez told The Associated Press. ''It's normal.''

However, one can never be so sure with knee injuries. His laundry list of previous ailments also isn't anything to be thrilled about and many would consider him a liability since he's owed $53 million over the next three seasons.

Colorado has a deep outfield with Corey Dickerson, Charlie Blackmon, Drew Stubbs and top prospect David Dahl. We'll see how Gonzalez's latest knee troubles will affect how the team handles that cast of players.