SANTA CLARA, Calif. (AP) -- The reeling San Francisco 49ers defense already had plenty to be concerned with this week before the added distraction of Aldon Smith's arrest.
First and foremost: Quarterback Andrew Luck, running back Trent Richardson and the new-look offense of the Indianapolis Colts.
The 49ers look to rebound from last week's tough loss in Seattle with a banged-up lineup.
San Francisco will be breaking in a new starting nose tackle against the Colts, has yet to gain clearance for starting rookie safety Eric Reid and has three other key starters who either missed practice or were limited this week with injuries.
However, a defense that ranked third in the NFL last season is accustomed to the adversity and welcomes the challenge of a Colts backfield strengthened earlier this week when the team acquired Richardson from the Browns.
Smith was arrested Friday morning in San Jose on suspicion of DUI and marijuana possession, but it was business as usual for San Francisco's defense as Smith practiced with the team later in the afternoon. Smith has been limited in practice all week due to a back injury.
Coach Jim Harbaugh said he expects Smith - second in the NFL with 3 1/2 sacks - to play Sunday, and the 49ers (1-1) appeared to be keeping their focus on bouncing back against the Colts after being routed 29-3 in Seattle.
''I don't think it's a distraction,'' cornerback Carlos Rogers said Friday. ''I think this team is strong. We're still salty about last week's loss instead of worrying about any problems that come up. We've got Indy, and that's our main focus. Everybody has to handle adversity when there's something wrong. If you have a hole in your roof, you patch it up.''
The 49ers are patching a hole in their defensive front created when starting nose tackle Ian Williams was lost for the season after breaking his left ankle against Seattle. He'll be replaced by Glenn Dorsey, who may be San Francisco's healthiest lineman Sunday. Tackles Ray McDonald (injuries to both ankles) and Justin Smith (shoulder) both missed practice this week and McDonald was listed Friday as questionable to play against the Colts.
Also questionable is Reid, who left last week's game in the second quarter after sustaining a concussion. Reid said he has passed all tests according to the NFL protocol for concussions and expects to return against the Colts. He still needs to pass a contact test before he can be cleared.
''I should be fine,'' Reid said. ''I didn't have a headache at all after the concussion, I felt perfectly normal. I wanted to go back in and play, but they hid my helmet.''
Reid has had a strong start to his NFL career with interceptions in each of his first two games and also has contributed with his rangy tackling in the secondary. The 49ers may need more of that against Indianapolis now that Richardson - who gained 950 yards rushing as a rookie last year with Cleveland - has been added to the Colts' arsenal.
Several 49ers said they expected Richardson to add a new dimension to the Indianapolis offense this week even though he practiced with the team for the first time Thursday. Reid is familiar with the downhill style of the stocky running back, having played against Richardson twice in college when Reid was at LSU and Richardson played at Alabama.
''You have to recognize that he's a good running back,'' Reid said. ''He's a hard runner always fighting for that extra yard. We know that it might take a little bit more oomph to get him on the ground. We're aware of the type of back he is. We have a pretty good defense, though.''
Linebacker Patrick Willis expects that defense to step up after faltering late against Seattle, which scored 24 points in the second half.The 49ers also had some defensive lapses during their season opener before prevailing 34-28 against Green Bay.
Willis and fellow All-Pro middle linebacker NaVorro Bowman will now be operating behind Dorsey, who was signed as a free agent during the offseason and has been worked in gradually to San Francisco's 3-4 defense.
''I have complete faith in Glenn's ability to play the nose and I'm looking forward to him there this week,'' Willis said. ''But no matter what the Colts do, it's all about us playing better defense than we've played in these first two games. It's always about being better the next week than you were the week before. So now our focus is on the Colts and winning.''