The San Francisco 49ers weren’t always looking at Keenan Allen. They were looking at his Indianapolis Colts teammate, Josh Downs.

General manager John Lynch told KNBR’s "Murph & Marcus" on Thursday that the team was “focused” on trading for the Indianapolis Colts wide receiver. While Lynch and head coach Kyle Shanahan were watching Colts film, Shanahan asked a different question: “What about Keenan?”

“And that started the conversation two and a half weeks ago,” Lynch said. “It’s a really good fit for us. And Keenan had a really good first day of practice.”

Lynch said the talks began alongside the DeForest Buckner trade negotiations, which resulted in the 49ers sending a fourth-round pick to the Colts for the veteran defensive tackle. At one point, he said, the Colts didn’t want to give up Allen, though: “It was more or less non-negotiable, but we kept communicating, and eventually it worked out.”

Downs, meanwhile, ended up going to the Kansas City Chiefs for fourth- and fifth-round picks.

Allen, 34, caught 40 passes for 351 yards and one touchdown on 58 targets in eight games with Indianapolis, which went 1-7 in those games. His last game with the Colts was a four-catch, 26-yard outing against Dallas on Sunday, the same Cowboys team the 49ers face in Week 10.

Lynch pushed back on the idea that Allen is insurance for Mike Evans, too, who has been dealing with Achilles and rib injuries.

“No, we just wanted to add a reinforcement there,” Lynch said. He pointed to Ricky Pearsall and Christian Kirk being out earlier in the year, and to rookie De’Zhaun Stribling being sidelined from the start. “With all those things, that position is vulnerable, and we just want to have enough guys, both in quantity and quality.”

Shanahan made the same point this week: “Even if Mike was good on all eight of these games, [it] wouldn’t have changed anything with trying to add another guy,” Shanahan said.

The challenge now is time. Lynch said Allen has to get through the playbook before Sunday. He noted that a veteran who has played in other systems has to translate what Indianapolis called a play into what San Francisco calls it. Allen “functioned well” in practice, Lynch said, and the staff, including receivers coach Leonard Hankerson, will give him what he can handle.

The newest 49ers pass-catcher will play alongside Jordan Watkins, Jacob Cowing, Demarcus Robinson and Brandin Cooks as well as tight end George Kittle and running back Christian McCaffrey. Evans is not expected to play, and Deebo Samuel, who missed the past several games with a hamstring injury, might be back.