"It's something that we've been paying attention to," general manager John Mozeliak said. "We even considered it a little bit at the Deadline."
Lopez, who has had an off season with the bat, struggled before he was given his release from the Nationals on July 31. Finishing his season in Washington with a .234 batting average, Lopez only hit .203 in June.
However, Lopez brings a little bit more power than current Cardinals infielders Cesar Izturis and Adam Kennedy. Averaging slightly over 10 home runs a year, Lopez knocked two out of the park in Washington this year, along with 25 RBIs.
"If you think about what he's done over the last few years, he's been a fairly productive offensive player," Mozeliak said. "Now, this year he's having a down year. But I think when you look at the numbers a little bit more than just the baseball-card stats, you see that there's maybe a little more to it. I think getting in this environment will put him in a better situation."
Mozeliak added the decision was primarily based on Lopez's versatility and because he brings "a different element to the offensive side of things."
In 2005, Lopez made his only appearance on the All-Star team as a member of the Cincinnati Reds. Hitting a career-high 23 home runs, Lopez also batted .291 with a .352 on-base percentage.
Lopez spent time with the Toronto Blue Jays (2001-2002), the Reds (2003-2006) and most recently since 2006 with the Nationals, who currently sport the worst record in the Majors at 42-71.
Brendan Ryan, who was optioned to Triple-A Memphis on Tuesday, also struggled mightily throughout the second half of the year. Batting as high as .316 in the middle of May, Ryan slumped over the next two months to a .242 average. Lacking a power bat -- he had no home runs and nine RBIs this year -- the move will give him some time to rediscover himself in Triple-A.
"[Lopez] provides a better player for that spot," said manager Tony La Russa. "Brendan is a young guy with a lot of future. When he was playing enough, it was kind of acceptable. But now, he isn't playing enough. Felipe is a better fit, ... Brendan's got his whole career ahead of him."
Carrying three other middle infielders in Izturis, Kennedy and Aaron Miles, who are all producing in different aspects of the game, La Russa said Ryan just happened to be the odd man out.
"The second baseman played pretty well today, the other guy is hitting .300 and Cesar is picking everything in sight," La Russa said of Kennedy, Miles and Izturis, respectively. "[Lopez] can play some outfield, play some second, short, he can also play third base. We'll see when he gets here."
Lee Hurwitz is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.