Left guard Adam Snyder sustained a right ankle sprain Tuesday that is expected to keep him out of this week's exhibition game against the Bears, coach Mike Nolan said.

Nolan said Snyder will be re-evaluated. No timeframe was given for his return. This means both of the 49ers' presumptive starting guards are now out of action. David Baas has not practiced due to a torn pectoral tendon, which he sustained in April.

The 49ers have not decided whom will replace Snyder in the starting lineup for Thursday's game against the Bears. Undrafted rookie Brian de la Puente has played left guard with the second team. Or the 49ers could insert rookie Chilo Rachal into the starting lineup at right guard and switch Tony Wragge to left guard.

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Nothing is new with the QBs. One writer asked Nolan if he'll be relieved whenever he finally names a starting quarterback.

Answered Nolan, "Not as much as you guys."

Nolan said no external influences -- such as salary -- will be considered when naming the starting QB.

"This decision is going to be based on who we feel at this point gives us the best chance to win," Nolan said.

For the record, here are the 2008 salary-cap figures for each of the "competing" quarterbacks:

Alex Smith: $9.916 million

Shaun Hill: $1.7 million

J.T. O'Sullivan: $491,000

Because O'Sullivan qualifies under the minimum-salary benefit as a veteran who signed a one-year contract, the 49ers are prohibited from signing him to a contract extension until March 2 at the earliest.

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