Giants manager Bruce Bochy said that Morse felt considerable discomfort after taking batting practice Tuesday and took the concussion test, which he failed.
"For him to be on the concussion list, I don't think it shocks any of us," Bochy said.
• Strickland (6 games), Harper (4) suspended
Said Samardzija, "That's the way it goes. It's unfortunate. He's a big piece of this team. He brings a lot of energy. It's tough to lose him."
Harper was grateful for the presence of Morse, a former Nationals teammate.
"As I was going out there, your first reaction is you might get blindsided by one of their players coming in," Harper said. "I'm kind of thankful that Mikey Mo and Samardzija collided, because Samardzija saw blood a little bit, I thought. I'm very thankful for Mikey Mo. That's a big spot with him coming in there. You never know. Their whole team's out there, and my team's coming behind me. You never know. I'm very thankful for Mikey Mo."
Chris Haft has covered the Giants since 2005, and for MLB.com since 2007. Follow him on Twitter at @sfgiantsbeat and listen to his podcast. This story was not subject to the approval of Major League Baseball or its clubs.