The MLS commissioner said that while the league is growing and has more new markets in mind, it must avoid the errors made by its predecessors.

FRISCO, Texas — MLS commissioner Don Garber says despite rapid growth, he still wants the league to expand slowly and not overextend its resources.

Minnesota United and Atlanta United will join the league in 2017, with expansion draft procedures announced Tuesday, while LAFC is set to begin play the following year. But the commissioner said avoiding the fate of the original North American Soccer League, which boomed in popularity in the 1970s but folded after the 1984 season, is still a priority.

"I go to sleep at night continually thinking that we should not make the mistakes of the NASL or other leagues who have expanded too quickly, so it would be a shame to take our eye off of that ball," Garber told reporters at Tuesday's U.S. Open Cup final. "But I don’t think we’re at that point yet. As you know, it’s 28 teams for us. We’re a long way from 28, still haven’t finalized our 24th team. So that gives us five more teams to fill over the next however many years."

That note, with MLS yet to finalize its 24th team, speaks to the troubles the league has had finding a suitable site for a Miami team, a franchise that was announced in 2014 but is yet to progress to the on-field stage.

That has happened while lower-division soccer has boomed in several cities around the United States. Minnesota United, currently competing in the revived NASL, will become an MLS expansion team in 2018, along with Atlanta United, another club in a market that once housed a modern-edition NASL team.

"When I look at what’s happening across the U.S. for the most part, because I think we’re fully expanded in Canada, and you see markets like Austin and San Antonio and San Diego and St. Louis and Sacramento and Las Vegas and Cincinnati, these are big cities that have fans that already are engaged with the sport on some level professionally," Garber said. "I don’t know how we don’t provide these fans and owners and municipalities the opportunity to be involved in MLS. We’ve got to be smart about it, careful about it."

While the league's growth is one story that consistently draws headlines, the league got plenty of attention last week when Landon Donovan returned to the field after nearly two years of retirement. For Garber, Donovan taking advantage of playing while he's still physically able is a good thing, and the extra media boost didn't hurt either.

"He’s one of the few players I actually have a relationship with," the commissioner said. "Our, kind of, careers have mirrored each other over the 17 years that I’ve been in the league. I’m happy for him. I hope it’s successful, a good decision and let’s see how it all plays out. But we certainly got a lot of attention. That’s not a bad thing for us."