After attempting to go for a slam dunk, he took an elbow to the head by Jayson Tatum.
The four-time MVP looked dazed as he checked to see if he had been cut.
He then headed back to the locker room flanked by security with under four minutes remaining of the second quarter of Game 2 and was subsequently booed by the Celtics fans.
James suffered a neck strain during the clash which was confirmed by a reporter on the Cavs’ twitter page.
But luckily for Cavs supporters, he was passed fit to continue.
After re-emerging from the locker room, he replaced George Hill with two minutes remaining of the second quarter and he was aggressive as he posted 25 points before half-time.
He was 4-7 with his three-point field goal attempts.
After a dismal display in Game 1 in which he scored just 15 points, James was back to his fluent best.
James also produced six assists and four rebounds before the break.
Cavs are looking to square the series in the Eastern Conference Finals after losing Game 1.