NEW YORK -- The NHL and NHL Players' Association will meet for a fourth straight day in an attempt to salvage a shortened season.

Key negotiators from the league and union, including NHL commissioner Gary Bettman and NHLPA executive director Donald Fehr, met for five hours Thursday and said talks will continue on Friday.

Thursday's talks were held at the offices of a midtown Manhattan law firm. So far, the sides have had little to say publicly about how the discussions have gone.

Sources told The Canadian Press that the Players' Association tabled an offer Wednesday night regarding revenue sharing and the league's "make whole" provision, which is designed to ensure all existing contracts are honoured in full. It is seen as the fundamental issue left to solve with the NHLPA having already agreed to see the players' share in revenue reduced to 50 per cent during the next CBA.

The union views that as a concession of more than US$1 billion because that's how much more players would earn if it remained at the current level of 57 per cent.

The league responded to the players' offer on Thursday, with Gary Bettman saying there's "still a lot of work to do."

With all regular-season games cancelled through Nov. 30, negotiations have reached a critical and delicate stage. Ten days will be needed from the time an agreement is struck until the season starts and there is still hope among the parties that a shortened schedule could begin by Dec. 1.

For that to happen, signs of progress need to emerge soon.

The sides have met for more than 20 hours over the last week, starting with an informal eight-hour session between deputy commissioner Bill Daly and NHLPA special counsel Steve Fehr in Chicago on Saturday. Larger groups that included owners and players spent more than seven hours together on Tuesday and another five hours on Wednesday.

Thursday's meeting was being viewed by both sides as extremely important. Other weighty topics, including revenue sharing and contract rules, were discussed by the NHL and NHLPA earlier in the week and still need to be worked out before the 54-day lockout comes to an end.

The push is clearly on now to see that happen.

Both sides have cleared their schedules and will continue to do so as long as positive momentum exists in negotiations. Daly had been scheduled to travel to Ottawa on Thursday to speak to a committee about sports betting, but ended up calling off the trip.