A federal judge in St. Paul on Monday ordered the National Football League to lift its lockout and allow players to return to work.

But the fate of the 2011 season remains in doubt as team owners filed an immediate appeal.

In her ruling in favor of the players' request for a temporary injunction, U.S. District Judge Susan Richard Nelson agreed that the lockout could irreparably harm them and their often-short careers.

The players, she said, "have met their burden of showing that it is likely that they will suffer irreparable harm absent the preliminary injunction.''

NFL officials continued to disagree and asked Nelson to stay the ruling pending an expedited appeal to the Eighth Circuit Court of Appeals.

In a statement issued Monday, the league said: "We believe that federal law bars injunctions in labor disputes. We are confident that the Eighth Circuit will agree. But we also believe that this dispute will inevitably end with a collective bargaining agreement, which would be in the best interests of players, clubs and fans."

Some players, including Minnesota Vikings kicker Ryan Longwell, weren't celebrating a final victory just yet.

"I really don't think it means much until the appeals court accepts or denies the ruling and keeps the lockout in place during the appeal," he said Monday.

While the ruling might have little immediate effect on whether the league resumes operations, the judge's injunction is a key victory in the players' efforts to be allowed to play while the sides continue their tug-of-war over a new collective bargaining agreement and how to divide more than $9 billion in annual revenues.

The lockout has been in effect since March 11, when talks on a new agreement broke down and players voted to decertify their union. A group of players, including the Vikings' Ben Leber and Brian Robison, then filed an antitrust lawsuit against the league and its teams.

For its part, the NFL has argued that it has a right to lock out the players and that Nelson should not step into the dispute while the National Labor Relations Board weighs a complaint by the league that players didn't negotiate in good faith. Nelson's ruling follows her efforts, and those of a federal magistrate judge she assigned as mediator, to get the league and its players to negotiate an agreement outside the courtroom.

The two sides met several times last week but could not come to an agreement. The sides are scheduled to meet again May 16. It is unclear what effect Nelson's ruling will have on the tenor or urgency of those talks.

'A big win' for players

Granting the injunction swings some of the leverage to the players' side, which could actually bring the two sides closer to a resolution, according to Seth Borden, a labor law expert at McKenna, Long and Aldridge in New York.

"It's still going to boil down to the way the parties view their respective positions and respective leverage," Borden said. "Until the league and the players feel like they're at the point of no return for next season, progress will be slow toward that overall resolution."

Robison agreed.

"It's a big win for us," he said. "I still feel like there's a lot of things that need to be hashed out, but it's definitely a big step in the direction we need to go. It makes us a little bit more confident about the way things are now. They'll search for a stay [of the lockout], they'll ask for an appeal. Hopefully, they will just shut them down period and say, 'Forget about it.' But even if they take that on, it definitely gives us a little bit better timeline."

According to ESPN, the players' trade association e-mailed players Monday suggesting they report to work on Tuesday, unless a judge stays Nelson's order. The sports network also reported that the NFL Management Council told teams to let players into their buildings, but also recommended keeping weight rooms closed.

A source told the Star Tribune that the Vikings staff will meet early Tuesday morning at Winter Park to review if they will allow players to use the facilities there.

Nelson's ruling did not immediately address the merits of the players' antitrust lawsuit, but another federal judge, U.S. District Judge David Doty, could soon leave his imprint on the likelihood of a 2011 NFL season. He is scheduled to hold a hearing May 12, during which he is expected to rule on whether the league can use more than $4 billion in television revenue it collected to help teams pay their bills if a season is not played. Players want that money placed in escrow.

At the end of her 89-page ruling, Nelson said one factor in her decision was the fact that the lockout hurts far more than just the players.

"The public ramifications of this dispute exceed the abstract principles of the antitrust laws, as professional football involves many layers of tangible economic impact, ranging from broadcast revenues down to concessions sales," she wrote. "And, of course, the public interest represented by the fans of professional football -- who have a strong investment in the 2011 season -- is an intangible interest that weighs against the lockout. In short, this particular employment dispute is far from a purely private argument over compensation."

Staff writer Chip Scoggins and the Associated Press contributed to this report. James Walsh • 612-673-7428