Vikings are trying to trade Tarvaris Jackson

The Vikings have called teams to see what they would be willing to offer in exchange for backup quarterback Tarvaris Jackson, according to a league source.

The Vikings have four quarterbacks on their roster, which must be trimmed to 53 players by Saturday. Coach Brad Childress said recently the team possibly could keep four quarterbacks, but it seems more likely that it will trade or release one.

Jackson has been the subject of trade rumors since Brett Favre arrived. However, it remains unclear which direction the Vikings will go if they are unable to trade Jackson.

Jackson, who started 20 games in his first three seasons with the team, admitted he feels a sense of uncertainty about his situation, but he said he is focused on preparing for Friday's preseason finale against the Dallas Cowboys.

"You never know with this business, period," he said. "I just take it as it is. Whatever happens, happens. I can't control it. I just try and get better, that's it. I can't worry about [whether he gets traded or released]. I'm not worried about it because I can't control it. Whatever is going to happen is going to happen whether I worry or not."

Childress said Favre will not play Friday (teams typically rest their starters for the final preseason game) so that means Jackson, Sage Rosenfels and John David Booty will split playing time.

"I feel certain that I can play well in this league," Rosenfels said. "When this team needs me, I can play at a very high level, and I think I've played pretty well this preseason. I think I've played well since we left Mankato and at the end of Mankato. I think I'm playing high-quality football. My goal is to continue to play at a high pace."

The Vikings dropped in value from $839 million a year ago to $835 million, according to Forbes magazine's annual NFL rankings. However, after three years of being last in these rankings, the Vikings are now second-to-last (or 31st). Oakland fell to the 32nd spot with a value of $797 million.

Lester Bagley, the Vikings' vice president of public affairs and stadium development, said the team would have no comment on the rankings. The team has been consistent through the years on not commenting about this list.

Owner Zygi Wilf bought the Vikings for a reported $600 million in 2005.

The overall article by Forbes paints a rather glum picture for many franchises operating in a rough economy, stating that a quarter of the teams are worth less than they were last year. It marked the first time in 10 years that any NFL team has experience a decrease in value.

The Vikings' issue is nothing new, according to the magazine, and involves the extremely limited revenues the team can generate at the Metrodome. The top team on the Forbes list is the Dallas Cowboys, who are worth $1.7 billion and just moved into a $1.2 billion stadium. The Cowboys also were No. 1 in 2008.

• Left tackle Bryant McKinnie did not practice Wednesday but his absence is not believed to be anything serious.

• Tight end Jim Kleinsasser returned to practice after suffering a hand injury in the preseason opener at Indianapolis. It's unclear how much work he was able to do because the media were allowed to watch only the early portion of practice.