"While lineup selections are made by each club's coaching staff, teams are expected to give their best effort in trying to win every game," Dan Courtemanche, the league's executive vice-president of communications, said by email Monday in a response to a Canadian Press query on the issue.
The league has never sanctioned a club for its lineup choice, he added.
D.C. United (3-21-6) shuffled its entire roster for Saturday's game in Toronto, with none of the starters from the previous week's game against New England featuring in the starting lineup.
Toronto (5-15-11) won 4-1.
"I set these guys up to fail today,'' coach Ben Olsen said afterwards. "It's pretty simple.
"We hung in there for about 60 minutes. Then I got some guys out that were going to maybe to factor into the Tuesday game. And now I'm putting guys out of position. You start adding those up and you're playing a real team in the MLS, that's what can happen. Our focus this week, the majority was on Tuesday and I set them up to fail."
Olsen, however, said his lineup choice was easy given his team's position in the league standings.
Courtemanche noted that Real Salt Lake, D.C. United's opposition in the cup final Tuesday, made 10 changes to its starting lineup Saturday in Vancouver and won 1-0.
Real Salt Lake (15-10-6) sits atop the Western Conference, but only six points separate first and fifth.
Real Salt Lake coach Jason Kreis acknowledged the importance of the cup final but said he was also concerned about the playoff run.
"Our playoff lives aren't secure," Kreis told the Salt Lake Tribune last week. "I don't feel like if we sit where we're at right now, we're going to make the playoffs. We need points and we need them in the worst way."
Had Vancouver (11-11-8) won, teams battling for the final playoff berth in the West might have had a legitimate complaint over RSL's lineup choice. A Toronto versus D.C. United matchup at the bottom of the East is of less import, however.
Given Real Salt Lake's status as an elite team in the league, one would also assume the quality of its reserves are well ahead of D.C. United's.