After that, it will be too late to add a postseason-eligible player from outside the organization. For some teams, help from the Minor Leagues will be coming starting Friday, when September roster expansion begins.
Here's a look at some of the recent developments on the waiver wire watch:
Dodgers: The Dodgers are looking to add another arm to their bullpen. They're also looking to add a hitter who can fill in at various spots and give the club another solid pinch-hitting option. Tampa Bay's versatile Greg Norton, who has filled in at four positions while hitting .306 for the Devil Rays, is among the players the Dodgers are considering.
Phillies: A month ago they were sellers, trading away outfielder Bobby Abreu, third baseman David Bell and pitchers Cory Lidle, Rheal Cormier and Ryan Franklin. Today, the resurgent Phillies are adding help for a September push. First, they picked up Jamie Moyer from Seattle, then Jose Hernandez from Pittsburgh.
Now, their latest move is the acquistion of veteran infielder-outfielder Jeff Conine and cash from Baltimore for a player to be named.
The Phillies are still looking for outfield help and would like to pry Juan Pierre away from the Chicago Cubs. Pierre could step in for Aaron Rowand, who is out for the rest of the regular season after breaking his left ankle.
Reds: The Reds signed catcher Javier Valentin to a contract extension for 2007 plus an option on 2008, but that won't make it any easier to deal catcher Jason LaRue. With Valentin and David Ross capably handling catching duties, LaRue is expendable, but the $5.25 million he is owed for next season has made it hard for the Reds to find a trade partner.
Cincinnati is looking for more pitching after closer Eddie Guardado went on the disabled list. The Reds, who have lost four in a row and lead the National League Wild Card standings by a half-game, sent pitcher Mike Burns to Boston on Monday for right-hander Tim Bausher and will continue to seek more arms.
Padres: San Diego picked up infielder Russell Branyan to give the club more power, but the Padres are still looking for pitching to fill the void created when right-hander Scott Williamson went on the disabled list due to a right elbow strain. In the meantime, the club recalled right-hander Jon Adkins from Triple-A Portland.
Red Sox: The Red Sox have been looking for left-handed pitching, more so now that Jon Lester has been placed on the disabled list. The Sox, six games out in the American League Wild Card standings and seven out in the AL East race, purchased the contract of first baseman Carlos Pena from Triple-A Pawtucket on Monday. Pena is expected to fill in while slugger David Ortiz returns to Boston for medical tests.
Tigers: The Tigers have been looking for another reliever, but they appear to have backed off in those efforts after calling up Andrew Miller, the club's first pick in this year's First-Year Player Draft. The Tigers are expected to use the left-hander in a relief role as they attempt to hold on to the top spot in the AL Central.