"I didn't fire on a pitch that was down the middle in BP," Myers said. "I knew then I was babying it. That's when I knew I probably wasn't going to compete in the game today."
The Brewers topped the Padres, 3-2, in the series finale.
Myers, who left Saturday's game after experiencing a cramp in his left calf while running to first base, first felt the tightness in his left forearm on Thursday.
When Myers decided he couldn't go, Green shifted Brett Wallace from third base to first base, Adam Rosales moved from second base to third base and Jose Pirela was inserted at second base.
"This was disappointing to scratch him at the last possible minute," Green said. "He wants to play every day. He wants to be out there, so I know it was frustrating for him to be honest about it and say, 'You know what? It is probably not best for me to play through this today.' Hopefully we are not dealing with anything after the off day tomorrow."
Myers is confident the injury isn't serious. He said the hindrance is strictly in his forearm and not in the wrist that has caused him problems throughout his career.
Jay injured his right shoulder while diving for a ball Thursday. Green expects the center fielder to be ready to play Tuesday, as well.
"Jon laid out two days ago in left-center field late in the game and kind of jarred his body a little bit," Green said. "I don't think there's anything that's a big deal there. He just kind of has a sore right shoulder at this point in time, but overall he feels good. He'll be fine. He just needed a few days down."
Andrew Gruman is a contributor for MLB.com based in Milwaukee. This story was not subject to the approval of Major League Baseball or its clubs.