Stokes looked in discomfort when he took a catch to dismiss Ireland's Curtis Campher during England's 10-wicket win in the one-off test at Lord's.
He has had knee trouble for some time now, restricting his seam bowling in test matches.
"I landed quite awkwardly. My weight went on the inside of my knee, I hyper-extended it. It was one of those things, but I am 32 (on Sunday) so that probably explains it," Stokes said.
"I bowled this morning, the first time I have bowled since being back from (the Indian Premier League) and I was really happy with the way it was. Nothing to worry about."
The all-rounder, who has picked up 194 test wickets, has bowled only 17 overs in his last four tests, while he bowled just one over for Chennai Super Kings in the IPL. He did not bat or bowl in the win over Ireland.
Stokes added that it was "never my intention to bowl in this game" but would be ready to share the ball when the Ashes get underway, with the first test against Australia at Edgbaston from June 16.
He also praised test debutant Josh Tongue after the seamer picked up a five-wicket haul in the second innings, dismissing top order batsmen at regular intervals. Tongue was named in the Ashes squad for the first two tests.
"He obviously played that third seamer role and we used him with different plans at different times," Stokes said.
"He bowled in longer spells and showed how versatile he can be, which is what we are looking for in a third seamer. He can bowl 90 mph, full and short...It was a special feeling for a kid to get a five-for on debut, particularly at Lord's."
