Hamilton and Alonso came to blows when the Mercedes driver tried to pass the Alpine driver for second place around the outside of Les Combes on the opening lap.
The seven-time world champion was forced to retire with damage after his car was sent airborne in the collision, while Alonso was able to continue and finished fifth.
Hamilton’s crash exceeded the Medical Warning Light threshold, which required him to make a visit the Event Medical Service, but Hamilton failed to do so.
The Briton did eventually go for a medical check, but only after Mercedes were informed that Hamilton could face further action if he did not.
“The Stewards received a report from the Race Director that driver Hamilton refused to visit the Event Medical Service following his crash on Lap 1 where the Medical Warning Light threshold was exceeded and only did so after the Race Director informed the team that further action could be taken if he did not,” the stewards’ notice read.
“This is not the first time this season that drivers (not Hamilton) have initially refused to go for a medical check. The Stewards issue a warning in this case, with a reminder to all drivers that stronger action may be taken in the future.”
Why Hamilton wasn’t penalised for crash
Hamilton did not receive any punishment for causing the collision with Alonso.
A statement issued by the FIA said: “The Stewards reviewed the video evidence and determined that Alonso was on the inside at turn 5.
“Hamilton’s front wheels were ahead of Alonso’s at the entry to the corner. Alonso moved his car off line to the inside with both right side tyres fully on the kerb and even somewhat inside the kerb.
“At no point did Alonso appear to lose control or understeer. Hamilton turned into towards the apex of the corner with Alonso still along side and the collision occurred.
“The Stewards considered that this was a first lap incident with a lot of movement relative to other cars in the first few corners, and thus take no further action.”