Dean McAmmond won't be returning to Colorado, but he won't be playing with Calgary either.

The NHL ruled Friday that the Calgary Flames forward is ineligible to play for the club for the rest of this season, but the trade that brought him back to Calgary was not voided.

McAmmond can still practise with the team, go to team functions and get paid his NHL salary, but he can't play in the squad's final 12 games of the season.

Calgary re-acquired McAmmond at the trade deadline Tuesday for a fifth-round draft pick. The Flames had originally traded McAmmond to Colorado on Oct. 1 as part of the Derek Morris-Chris Drury deal.

The trade was thrown into doubt late Wednesday after it came to light that the transaction violated a clause in the collective bargaining agreement.

"The player technically was not eligible to return to Calgary," Bill Daly, NHL executive vice-president and chief legal officer, said in a statement Friday. "The Flames traded McAmmond to Colorado on Oct. 1, 2002, three days prior to the NHL waiver draft, and Article 13.36 of the collective bargaining agreement states explicitly that 'a player traded by a club within the four weeks prior to the waiver draft may not be re-acquired by such club within the forthcoming season.'

"After becoming aware that the transaction had been concluded in error, we consulted with the clubs involved in the trade and determined that while a reversal of the trade was not required, the player nonetheless will not participate in league play for Calgary for the balance of the season," Daly said.

The reason the rule exists is so teams don't try anything strange at the annual waiver draft, like making pre-arranged deals with teams for players they don't want to lose in the draft.

In the past, some NHL teams would trade a player they didn't want to expose in the waiver draft and then re-acquire him a few weeks later for a low draft pick. In practice, it was called "hiding" players.

Normally the league would catch a glitch such as the McAmmond trade, but because of the extraordinary amount of deals at the deadline -- 24 deals involving 46 players -- the NHL's front office staff didn't catch the little-known rule.

Though the Flames are out of the Western Conference playoff picture, the loss of McAmmond for the remainder of the season hurts them nonetheless.

The 29-year-old forward, who has 10 goals and eight assists in 41 games this season, had 21 goals and 30 assists in 73 games with Calgary last year and clicked with Flames' stars Jarome Iginla and Craig Conroy.

Flames general manager Craig Button said he should have never traded McAmmond in the first place.