San Francisco signed the running back and special teams standout to a one-year contract Friday.
The team made the announcement soon after reports emerged that the Niners and coach Jim Harbaugh had worked out quarterback Peyton Manning at Duke on Tuesday night. A person with knowledge of the workout confirmed it happened, speaking on condition of anonymity because the session hadn't been made public.
"I think Alex is a great guy. I think we've got a great quarterback in Alex," Cartwright said. "Whoever is there, we'll be there to support him. Right now Alex is the guy."
The 49ers had been working to re-sign Smith, the No. 1 overall draft pick in 2005 who made a comeback in 2011 under first-year coach and former NFL QB Harbaugh, and Smith has acknowledged he was happy with the three-year offer.
Smith and Manning both are represented by agent Tom Condon and CAA Sports.
"Alex is trying to figure out what he wants to do," 49ers CEO Jed York said earlier this week. "There have been good conversations back and forth."
An email to Smith, multiple messages to his agency and his father have gone unreturned. The 49ers have declined to comment on their interest in Manning one way or another.
The 27-year-old Smith threw for 3,150 yards and 17 touchdowns with only five interceptions as San Francisco went 13-3 and ended an eight-year stretch during which the 49ers didn't reach the playoffs or post a winning record.
San Francisco went 6-2 on the road and won four of those games in comeback fashion - and Smith rallied his team from behind five times in all, not to mention a 36-32 victory against the favored Saints in the NFC divisional playoffs. Smith completed a 14-yard touchdown pass to Vernon Davis with 9 seconds left to seal it after Drew Brees had put his team ahead.
When asked if Smith is still the man, Gore said, "I think he is."
Signing Manning - and not bringing back Smith - could be a risk considering his multiple neck surgeries if he happened to get hurt in training camp and San Francisco was left with unproven backup and second-year pro Colin Kaepernick.
The NFC West champion 49ers on Monday signed wide receiver Randy Moss after he spent a year out of football, hoping he will be the dynamic wideout and deep threat of his past to open up the field.
"We are extremely pleased to re-sign an All-Pro player like Carlos," said general manager Trent Baalke. "His leadership and performance were integral to our success as a team. We look forward to his continued contributions, both on and off the field."
"Rock has been a standout special teams contributor, who has also shown versatility at the running back position," 49ers general manager Trent Baalke said. "He has all of the intangibles that we look for in a 49er."
AP Sports Writer Joedy McCreary in Raleigh, N.C., contributed to this story.