Hamilton was leading his team-mate Russell through the famous Eau Rouge-Raidillon ascent but the seven-time world champion appeared marginally slower and off-line through the left-right.
Towards the top of the hill, Hamilton drove off the circuit, drifting over the painted run-off before rejoining marginally ahead of Russell, who lifted off the throttle in response.
Hamilton was placed under investigation as a result, and now both drivers have been summoned to report to the race stewards.
Specifically, this is in relation to an alleged breach of Appendix L of the 203 FIA International Sporting Code.
The clause in question reads: "Drivers must use the track at all times and may not leave the track without a justifiable reason.
"For the avoidance of doubt, the white lines defining the track edges are considered to be part of the track but the kerbs are not.
"Should a car leave the track for any reason, the driver may rejoin. However, this may only be done when it is safe to do so and without gaining any lasting advantage.
"A driver will be judged to have left the track if no part of the car remains in contact with the track.
"A driver may be reported to the Stewards should they perform any act which results in debris being brought onto the track."
Hamilton ended the qualifying shootout for the Sunday race in fourth. But he will start the GP from third owing to a five-place grid penalty for Max Verstappen, who was fastest over Ferrari's Charles Leclerc by 0.82 seconds. Russell, meanwhile, ended Q3 eighth quickest.
The Mercedes duo notably also had a brush during Q2 of the Spanish GP earlier this season. Then, Hamilton sought to pass Russell on the main straight but the #63 machine drifted over to the edge of the track.
The W14s made brief contact to sustain minor bodywork damage, while Hamilton took to the grass.
Russell and the team were handed a formal warning having "abnormally changed direction".
