The left wing-back broke the deadlock for Chelsea in Saturday's 3-1 win over Arsenal, beating Bellerin in an aerial challenge.
But Alonso's momentum and height saw him catch his opponent with an elbow to the face.
Should Chelsea's goal have stood after this challenge on Hector Bellerin?
Sat, February 4, 2017
Should have Chelsea's opening goal against Arsenal stood after this challenge on Hector Bellerin
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Should Chelsea's goal have stood after Alonso's challenge on Bellerin?
Bellerin was forced to come off with concussion and after the match Arsenal boss Arsene Wenger was adamant the incident was foul.
However Alonso has since taken to Instagram to celebrate the win and wish the Spaniard a speedy recovery.
Marcos Alonso beats Hector Bellerin to the ball
He said: "Another great day at the Bridge yesterday.
"Also hope to see my homie @hectorbellerin back on the pitch soon. Unlucky challenge."
Hector Bellerin suffered a concussion
Yesterday Bellerin assured fans he is "recovering well" following the challenge.
He wrote on Instagram: “Thank you for all the messages.
"I'm recovering well at home and will soon be back on the pitch to help the team fight back!"