SAN FRANCISCO �” In the 20 months since Eric Johnson last played in an NFL game, he considered quitting football, spent countless hours in rehabilitation �” and lost his job as the San Francisco 49ers’ starting tight end to a rookie expected to be a star for years.

So it’s no wonder Johnson is a bit anxious about the 49ers’ exhibition opener against the Chicago Bears tonight.

At least he’s not alone: Several players on both sidelines at Candlestick Park will be eager for the first chance to show their careers are back on track.

“I’ll definitely be nervous, but I’m always nervous before a game,” Johnson said. “You just have to focus. Everything is behind me. I’m not looking to the past at all, but it’s part of what got me back here again.”

Johnson has missed two of the last three seasons with injuries. He sat out every game last season with foot injuries, including a torn muscle �” and to add a bit of anxiety to Friday’s game, he missed all of 2003 when New Orleans’ Dale Carter broke his collarbone on the first play of the 49ers’ first exhibition game.

Once he gets past that nerve-racking first play, the Yale graduate hopes he can get back to the form he showed in 2004, when he was San Francisco’s leading receiver with 82 catches for 825 yards. He’ll have to do it in a variety of roles, because the 49ers drafted Maryland’s Vernon Davis with the sixth overall pick last spring.

But after spending much of the last three years in rehab, Johnson isn’t giving up yet. He’ll be among dozens of players hoping to make an impression on coaches in the clubs’ prelude to a regular-season rematch on Oct. 29.

“I envision a lot of two-tight end sets,” said Johnson, who also has lined up as a wideout and a fullback in offensive coordinator Norv Turner’s new scheme. “Having Vernon and myself in the lineup will give us plenty of flexibility.”

Chicago quarterback Rex Grossman might feel some of the same anxieties when he steps under center for the Bears, who begin a season of high expectations after winning the NFC North and reaching the playoffs.

Grossman broke his ankle in the Bears’ second exhibition game last season, undergoing surgery and sitting out the first 13 games while Kyle Orton improbably pushed Chicago toward the playoffs.

Grossman returned for the final regular-season games and a playoff loss to Carolina, finally showing some of the promise Chicago still believes he possesses. But after getting injured early in each of the last two seasons, the fourth-year pro is eager to stay healthy long enough to cement his starting spot �” particularly with veteran Brian Griese on the bench behind him.

“I’m real excited about Friday night,” Grossman said. “It’s our first chance as a unit, in 2006, to really get something special started.”

Running backs Cedric Benson and Thomas Jones will sit out for Chicago, nursing fairly minor training-camp injuries. Adrian Peterson will start, but coach Lovie Smith doesn’t plan to play his starters much beyond the first quarter, leaving plenty of time for rookie prospects P.J. Pope and Andre Hall.

San Francisco quarterback Alex Smith is expected to play most of the first half �” and the former No. 1 pick agrees he can use the work. After throwing just one touchdown pass in his tumultuous rookie season, he’s eager to find a groove with three talented targets he didn’t have last year: Johnson, Davis and new receiver Antonio Bryant.

“It’s been a long time since this team has been out on the field,” Smith said. “We’re a very different team now. It’s going to be fun to see where we’re at in the development process in this game.”

The Bears also are looking forward to a break from training camp in Bourbonnais, Ill. Their defense, which allowed the fewest points in the NFL last season, could get off to a great start against an offense that �” while markedly improved �” finished dead-last statistically last year.

“We haven’t really tackled anyone live yet,” Lovie Smith said. “You want to go against an opponent, and we have a good one coming up. We play them during the regular season, so this is a big game for us.”