The National Football League kicks off Sept. 8, and with it will disappear hours and hours that some 21 million U.S. workers pour into fantasy sports leagues.

Not to worry, say employment consultants Challenger, Gray & Christmas. Employees may spend as much as nine hours a week plotting and planning their moves, but the actual impact on productivity will be small.

"In an information-based economy, productivity is very difficult to measure," says Challenger CEO John Challenger. "And the same widespread access to the internet from our desks, phones, and laptops that allows people to manage their fantasy teams from any place at any time, also allows work to be completed outside of traditional 9-to-5 work hours."

Challenger actually suggests that employers encourage company leagues to boost morale and output, claiming that "in the long run, this may lead to increased employee retention." Other research has found that fantasy sports strengthen relationships between co-workers, and 20 percent of players in a 2006 Ipsos survey said playing fantasy sports helped them make a valuable business contact.

Nineteen percent of all full-time U.S. workers are fantasy sports players, says the Fantasy Sports Trade Association. The average player belongs to 2.5 of the some 70 million free and paid leagues operating in the U.S. and Canada, according to the association. Membership has leaped 60 percent in the past four years to 32 million players, with 80 percent of them involved in football.

A Challenger survey last year found that most fantasy participants didn’t find playing in a league to be very distracting. On a scale of one to 10, where one represented no influence on productivity, nearly 70 percent of players chose four or below. Less than eight percent of respondents rated the distraction a seven or an eight, and none gave it a nine or a 10.

Says Challenger: "If you look at a company’s third and fourth quarter earnings statements, it is unlikely that you will find a fantasy football effect."

He added: "An across-the-board ban on all fantasy football or sports websites could backfire in the form of reduced morale and loyalty. The result could be far worse than the loss of productivity caused by 10 to 20 minutes of team management each day."