According to manager Dale Sveum, Valbuena injured himself 4-5 days ago and then re-injured himself pinch-hitting on Friday.
Watkins, 23, was hitting .243 with an on-base percentage of .333 at Triple-A Iowa this season after being the Cubs minor league player of the year in 2012 when he produced a .383 on-base percentage at Double-A Tennessee.
"That's a big part of my game, drawing walks," Watkins said before his major league debut on Sunday against the Los Angeles Dodgers. "I just grind. I'll see a lot of pitches."
Watkins had 52 walks in Iowa this year after drawing 76 at Double-A the year before. He'll start at second base on Sunday next to shortstop Donnie Murphy as Starlin Castro is being given his second day off of the season.
Murphy was recalled on Saturday. He and Watkins have played together all season at Triple-A Iowa.
"It's going to be nice having him there just for comfort factor," Watkins said. Sveum said he was planning on giving a day off to starters Darwin Barney and Castro and it just worked out that Sunday was it for both of them.
Watkins will mostly come off the bench for the Cubs, though Sveum left open the possibility that Barney could play shortstop and Watkins second next time he gives Castro a breather.
"He's an exciting player that can run," Sveum said of Watkins. "Left-handed hitter that can drive the ball but he's always got on-base. I'm anxious to see him play up here."
Watkins admitted it's been a "rough year" referencing his .243 batting average and a "bad week on defense." But after arriving in Seattle for a series against Tacoma over the weekend he was happy to get the call to come up to the Cubs.
"We had just got into our hotel in Seattle and my manager called me," Watkins said. "To be honest I didn't have his number in my phone so I was like 'What number is this?' so I didn't answer. Then he called right back again and he told me I was going. I thought he was joking but he was serious."
The Cubs will try to avoid getting swept by the Dodgers with a makeshift lineup on Sunday as three regulars will get the day off.
"It fell into place today," Sveum said. "Obviously we're not doing much offensively, so just give guys a chance to kick back."