Cruz, who will join the Nationals on Wednesday, will be the everyday shortstop, while Guzman will be a defensive replacement. Entering Tuesday, Cruz was hitting .268 (56-for-209) with five home runs and 19 RBIs in 81 games for San Francisco.
"He will start playing as soon as he gets here," Robinson said.
Cruz, 32, is best remembered for his days with the Tigers from 1997 to 2001. His best season came in 2000, when he hit .302 with 10 home runs and 82 RBIs.
Cruz will be a free agent after the season and is making $800,000 this year. The Nationals will pay $136,000 of that salary.
"We haven't scored any runs. Deivi has played some shortstop, second and third base," Bowden said. "He is hitting .268, a little bit of offense.
"I need to give [Robinson] some choices. Between this trade and our callups on Thursday, he has some more choices. We are going to have some fresh legs and some fresh bodies. Maybe they will spark the guys we have now. ... We are going to do what we can to jumpstart us and get some energy. It gives us some depth. It gives us protection."
Cox, 23, was the Expos' 19th-round pick in the 2004 First-Year Player Draft. He was 4-4 with six saves and a 3.00 ERA in 42 games out of the bullpen for Class A Savannah.
With the acquisition of Cruz, Washington must send somebody down to the Minor Leagues, and right-hander Jason Bergmann is the leading candidate for the demotion.
Bergmann, who was called up last Saturday, has appeared in two games and pitched 3 1/3 innings, giving up no runs and striking out five batters. He won his first Major League game on Tuesday.
However, look for Bergmann to be back with the Nationals sometime next week.
Bergmann, 23, went a combined 5-2 with seven saves and a 2.19 ERA in 41 games out of the bullpen for New Orleans and Double-A Harrisburg. He also fanned 76 batters in 74 innings en route to posting a 2.6-to-1 strikeout-to-walk ratio.
More on Drese: Right-hander Ryan Drese, who is out for the season because of a torn labrum, has been playing with the injury since he was with the Rangers early this season.
"He was able to pitch with the tear. His lack of performance had to do with the tear," Bowden said.
More callups: On Sept. 1, look for the Nationals to bring up as many as 10 players, including third baseman Ryan Zimmerman, outfielders Brandon Watson, Kenny Kelly and Tyrell Godwin and reliever Bill Bray.
The Nationals were hoping to bring Zimmerman up before the roster expanded, but injuries to the relievers prevented that from happening. However, if the Nationals make the playoffs, they can put somebody on the disabled and put Zimmerman on the roster.
Zimmerman is likely to be the regular third baseman once he is promoted.
Watson, Kelly and Godwin are expected to come off the bench as pinch-hitters. All three players had Major League experience with the Nationals this season.
Bray was the Expos' first-round pick in the 2004 First-Year Player Draft. He is currently playing for Triple-A New Orleans. He is 1-4 with a 4.00 ERA. He has struck out 21 batters in 18 innings.
On deck: The Nationals play a doubleheader against the Braves on Wednesday afternoon starting at 4:35 p.m ET.
Right-hander Esteban Loaiza (9-9, 3.57 ERA) will get the start in Game 1. In his fourth matchup against the Braves this season, Loaiza will face Horacio Ramirez (10-8, 4.52 ERA). Loaiza has yet to pick up a decision, but he has a respectable 3.32 ERA against Atlanta. In his last start, Loaiza pitched seven solid innings and gave up one run on three hits against the Cardinals, as the Nationals won the game, 4-1.
In Game 2, Livan Hernandez (14-6, 3.87 ERA) will get the nod for the Nationals and take on John Thomson (3-4, 4.97 ERA). Hernandez will try to bounce back from his last two rough outings, in which he has given up 12 runs over eight innings. His ERA has soared from 3.45 to 3.87 over those two starts.