The tourists posted 365 for seven to draw with the Sri Lanka Board XI, with Joe Root retiring out following an untroubled century, but that and the question marks over Keaton Jennings and Joe Denly in the top three were secondary concerns to Nissanka's well-being.
The 20-year-old was crouching for cover when a powerful Jos Buttler pull thudded into the top of his head, leading to a lengthy interruption in play and an early tea after Nissanka was led from the field on a stretcher and taken to hospital.
England's team doctor Moiz Moghal, physio Craig de Weymarn and massage therapist Mark Saxby were among those who assisted in his on-field treatment, carefully bracing his head and placing him on the stretcher.
Buttler had actually been given out after the ball looped up off Nissanka's helmet to Angelo Mathews at leg-slip, but the England batsman remained in the middle as players from both sides looked on in concern.
Nissanka was said to be conscious as he left the Nondescripts Cricket Club but complaining of neck pain ahead of a planned MRI scan.
The fielding side were shaken enough to avoid posting any close catchers for the remainder of the match, almost unheard of to spinners in this part of the world.
Stokes returns after injury alarm
His travails made light of an earlier false alarm over Ben Stokes, who was forced to retire hurt on 10 in the afternoon session when he was struck on the left arm by a Lahiru Kumara short ball.
Stokes showed no initial discomfort, briefly attempting to bat on before opting to head for the dressing room.
Nothing more serious than bruising above the shoulder was found and he resumed his innings after Root's retirement, adding a further 21 runs before being caught at slip reverse-sweeping.
England would have been happy to see the Test skipper reach three figures, and do so by barely breaking sweat, while Moeen Ali (60) and Buttler (44) also banked valuable time in the middle.
But the real intrigue lies at the top of the order, missing the retired Alastair Cook for the first time in 12 years.
His decision to step off the stage probably saved Jennings from the axe but the Lancashire opener still has plenty to prove after a lean summer.
He batted almost an hour here, eking out 13 runs before dragging Shehan Madushanka into his stumps. The 26-year-old's reaction told a story, pivoting sharply on his heel and swinging his bat in frustration.
At the other end newcomer Rory Burns was progressing serenely in his first knock in an England shirt. He met the ball cleanly, drove confidently down the ground and showed a pleasing intent to score against spin.
He hit nine boundaries in his 47 and was easing to a half-century when a miscommunication with Denly saw him run out. By then a Test debut in Galle on Tuesday had moved from likely to virtually certain.
Denly's hopes of making his own bow did not rise as sharply. The Kent all-rounder outscored Jennings with 25 from number three but batted awkwardly for much of his 52-ball stay, including dicey moments from each of his first two deliveries.
His selection prospects may yet hinge on wicket-keeper Jonny Bairstow, who remains a doubt for the series opener but batted and performed keeping drills in the nets.
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