"I'm out of the championship, for sure," Hamilton said post-race. "There is no question about that. But I'll still keep working as hard as I can to try and pull it back together somehow."
Hamilton was ultimately unable to improve much on his 14th-placed position on the starting grid at Imola, spending most of the race chasing Alpha Tauri driver Pierre Gasly while also being lapped by Red Bull rival Max Verstappen.
The seven-time world champion had finished 13th at Friday's rainy qualifying session, and then dropped back one position further after a disastrous performance at Saturday's Sprint Qualifying -- a controversial new format that has been added to three weekends this season.
Speaking about the result, Hamilton added: "We all feel it as a team."
'Trying to move forward'
Hamilton finished nine positions behind Mercedes teammate George Russell, who came in fourth -- making him the only driver to achieve a top-five finish at every race so far this season.
"At least, George got some points for the team today. My apologies to everyone that I wasn't able to do the same," Hamilton said.
"Everyone's just head down trying their best, there's no one that's giving up, everyone is trying to move forward as fast as they can. (I was) just bit of a sitting duck today."
It was Red Bull who dominated the podium on Sunday, with Verstappen and teammate Sergio Pérez finishing in first and second place respectively. McLaren's Lando Norris trailed behind in third.
Meanwhile, Ferrari were unable to capitalize on their home advantage. Championship leader Charles Leclerc finished in sixth after spinning off the track, while teammate Carlos Sainz crashed out on the first lap.
Plagued by porpoising
Mercedes have been plagued with ongoing car issues this season, including porpoising -- a phenomenon where a car achieves its top speed and then bounces up and down on its suspension.