MANKATO -- Benny Sapp opened training camp as the odds on favorite to win the job as the nickel back in the Vikings defense.

But the cornerback hasn't been able to take part in the competition with Asher Allen since Sunday. The Vikings have been holding Sapp out because of post-dehydration symptoms.

Sapp did not want to get into specifics of what is wrong on Thursday, but the problems started on Saturday morning when he had to leave the field after becoming dehydrated on what was a hot day. Sapp actually returned to that practice but clearly the Vikings became more concerned about the situation afterward.

“I feel a lot better," Sapp said after watching the afternoon practice Thursday. "I’m just waiting if they give me the OK to get back out there.” Sapp does not know exactly when he will return and made it clear it's up to head athletic trainer Eric Sugarman and his staff. "I just let them deal with it and just go day-by-day and let them tell me what they want me to do," he said.

The Vikings don't take any chances with dehydration and players getting overheated. Coaches can often be heard telling players during breaks in practice to get water into their system and a major emphasis is placed on the issue of hydration in a meeting just before training camp opens.

Meanwhile, running back Darius Reynaud did not practice today after suffering what appeared to be an injury to his left foot on Wednesday. Reynaud was taken off the field on a cart, but that's pretty standard procedure for the Vikings when they want to take an injured guy to the locker room for an examination. In other words, just because a guy leaves on a cart doesn't mean it's a serious injury.

Finally, the Vikings afternoon practice was a 10-10-10 session that was conducted in shells and shorts. Running back Adrian Peterson (leg), wide receivers Percy Harvin (death in the family) and Sidney Rice (hip), cornerback Cedric Griffin (knee) and linebacker J Leman (leg) were among those who sat out.