TUKWILA – Call it a turf war.

Sounders FC’s home game Saturday against Toronto FC could feature a half-dozen world-class stars, many of whom will participate in this summer’s World Cup in Brazil. But something much different was the center of attention Monday — the aging artificial turf at CenturyLink Field.

What turned into a leaguewide debate began when Toronto FC coach Ryan Nelsen said his lineup choices, in regard to players returning from injury, would be affected by the turf.

“It’s tough,” Nelsen told reporters. “You’ve got the travel and then you’ve got not just an artificial field — it’s a bad artificial field.”

The implication was that Michael Bradley and Jermain Defoe, TFC’s two prize offseason acquisitions, could be uncertain to play, even if both players claimed this week they have recovered from minor injuries.

When told of Nelsen’s comments, Sounders FC coach Sigi Schmid said natural grass is always soccer’s preferred surface but took issue with an apparent singling out of Seattle’s turf, which is entering its third season of use.

“Let me say this first, tell me which turf field is good in this league,” Schmid said. “There is no good turf field in this league.

“I don’t disagree, necessarily, with Ryan’s statement. I’d love to have brand-new turf this year, as would everybody else. But I disagree with the point of making it seem like Seattle’s is worse than the others. I think the others are equally as good or as bad — however you want to look at it.”

Other teams with artificial turf are Portland, Vancouver and New England, though the Timbers installed new FieldTurf before this season.

In response to Schmid’s comments, Portland owner Merritt Paulson defended his team’s turf on Twitter, arguing there is much less use by its home teams and fewer events like concerts. He also used the fact that New York star Thierry Henry, a notorious turf critic, has played in Portland but never Seattle to illustrate the quality of the Timbers’ synthetic surface.

Adrian Hanauer, Sounders FC’s part-owner and general manager, explained in January why the FieldTurf in Seattle would not be replaced, even though the previous installation was well-worn in its third year.

“Our intentions are to replace the field every (two to three) years, or whenever it is needed,” he wrote in an email. “The field crew, the Sounders and the Seahawks continually assess the quality of the field and we believe that the field is still in top condition.”

Even so, Schmid said last week the turf this year is “not as good as it was last year. It’s not as good as it was in its first year.”

So, as Nelsen implies, is there a real injury concern at CenturyLink Field?

Schmid said players’ bodies eventually get used to the physical strain of playing on turf, and that the surface would be an issue for someone with chronic knee issues, for example. It is no accident, then, that the Sounders often practice on grass throughout the week.

“A grass field is ideal — a good grass field — but a good turf field is not more dangerous than a bad grass field, necessarily,” Schmid said.

Some new Sounders have said the artificial turf requires adjustment, but midfielder Marco Pappa noted that ultimately everyone has to deal with the same conditions. Goalkeeper Stefan Frei explained there are positives to the surface, too.

“One thing that turf should give you is consistency once you figure it out — how it skips,” Frei said. “It’s pretty fast, to be fair, so hopefully I’ll get used to it.”

Joshua Mayers: 206-464-3184 or jmayers@seattletimes.com. On Twitter @joshuamayers.