[MLS] The rapid progress shown by goalkeeper Sean Johnson last year in his rookie season and the new MLS rules regarding rosters has prompted the Chicago Fire to waive keeper Andrew Dykstra, who had been the heir-apparent to former Fire goalie Jon Busch.

Chicago surprisingly waived Busch just a few days prior to the start of the 2010 season, opening up the starting slot for Dykstra. But he wasn’t able to hold off rookie Johnson, who played 13 games and posted three shutouts and a 1.31 goals-allowed average. Dykstra’s stats were slightly better (17 games, 1.24 GAA) but Johnson’s spectacular yet steady play endeared him to Fire players and fans as well as U.S. coach Bob Bradley, who gave him his first senior team call-up and cap Jan. 22 against Chile.

When the Fire traded a third-round pick in the 2011 SuperDraft to Toronto FC in exchange for veteran goalie Jon Conway, Dykstra’s fate was sealed. The new MLS roster regulations require teams to carry three goalkeepers, one of which must fill a developmental slot. That player must be younger than 25 for the entire season. Dykstra turns 25 on Wednesday.

Though Johnson is only 21, he’s on the regular roster, as is Conway.

“We’re in a situation where Sean [Johnson] is our starter going into 2011 and we wanted to add someone with the experience needed to push him and also fill in for him in case of injury or national team call ups,” said technical director Frank Klopas to mlssoccer.com. “We feel we got that player during the draft in Jon Conway.”

The Fire opened preseason training this week with more than 40 players, about 30 of which will head to Florida next week for the second phase of preseason.

On Monday it named its new captain: Midfielder Logan Pause, a veteran of 198 games for the club since being claimed as the No. 24 overall pick in the 2003 SuperDraft out of the University of North Carolina. He’s also been capped six times by the USA.