Ericsson, who has remained Alfa's reserve after losing his race seat with what was then Sauber at the end of last season, is skipping this weekend's Portland IndyCar round to be present at Spa.

Sources had suggested this was due to a specific concern over whether Raikkonen would be available for the race.

Read Also: Ericsson on standby for Alfa Romeo at Belgian GP

The Finn confirmed this was the case in the Spa paddock on Thursday.

"I pulled a muscle and we will see how it is," said Raikkonen. "We need to have some back-up plan. In my head it should be fine but you never know.

"It would be stupid not to have our third driver in case I couldn’t be driving, then it is the worst case scenario.

"There is a reason why every team has a third driver. It is a normal story. It is a difficult situation for him also because he had a race, but that is how it is."

Raikkonen did not elaborate on how he had sustained the injury: "Sport. It is dangerous. I always said it is more dangerous – drinking is probably safer. Usually you don't get injured, you just get a hangover."

Ericsson is bidding to secure a new deal to continue in IndyCar for 2020, but skipping the Portland race for an unnecessary appearance at Spa represents a frustrating interruption to his efforts in the United States.

Ericsson will be replaced in the Schmidt Peterson Motorsports IndyCar line-up by Conor Daly for this weekend's race.