Strasburg was examined by a doctor after Monday night's loss to the Braves, and the team said he was suffering from tightness in his forearm.
Rizzo said Strasburg's surgically repaired right arm is "structurally perfect," according to the newspaper. He added that he suffered some irritation that might be related to using a muscle-stimulation machine prior to his start. Strasburg had Tommy John surgery in 2010, but Rizzo said this issue has nothing to do with that injury.
"He's strong as an ox," Rizzo said, according to the Post.
Nationals manager Davey Johnson also said the electrical stimulation machine may have been the reason Strasburg experienced discomfort.
Johnson added the Nationals do not expect Strasburg to have continued problems with the irritated nerve but it was too early to determine whether Strasburg will make his next scheduled start Saturday at Pittsburgh.
Strasburg insisted Monday that he won't miss a start.
"I'm not missing my next start," he said. "I'll tell you that right now."
Strasburg had lost a career-worst four straight starts before pitching six innings and getting a no-decision in the 3-2 loss. He is 1-4 with a 3.13 ERA.
Strasburg appeared to struggle to get comfortable on the mound, sometimes shaking his arm after a pitch.
Johnson said Strasburg "doesn't look right to me."
Strasburg gave up two runs and six hits, walking four and striking out eight.
"His command was way off, so I knew something was off," Johnson said.
Atlanta beat the Nationals for the eighth straight time dating to last season. The Braves swept three games at Washington earlier this month.
The loss hurt, but Johnson's mind was on Strasburg's health.
"He was shaking his elbow more frequently," Johnson said, adding Strasburg didn't complain "but he was irritable."
"I was really concerned," Johnson said. "Any other time, I might have let him continue. Hopefully, it's no more than a tired arm or something."
Strasburg insisted he "felt good" physically but struggled with his control.
"I couldn't throw strikes early on," Strasburg said. "I was able to kind of battle through it and keep it close."
Asked why he was shaking his arm, he said, "You just try to stay loose."
Information from The Associated Press was used in this report.