Jeff Gordon to return to NASCAR if Dale Earnhardt Jr does not recover

Earnhardt withdrew from this weekend's Loudon race on Thursday night, with Alex Bowman called up from his JR Motorsports Xfinity Series team as stand-in.

But Hendrick Motorsports general manager Doug Duchardt said recently-retired five-time Brickyard 400 winner Gordon will make a comeback for Indy if Earnhardt continued to be absent.

"He's a four-time champion and has 93 wins, he's not a bad person to put in the car, but this week he's in France," said Duchardt of Gordon.

"The way the week played out, we thought we only needed a back-up driver.

"If Dale is not able to go at Indianapolis, we will put Jeff Gordon in the car.

"When Dale is ready, that's his car to get back into."

Earnhardt missed two races with concussion in 2012, and suspects crashes in the recent Michigan and Daytona rounds might have led to a recurrence of the symptoms.

He felt unwell in the build-up to last weekend's Kentucky race, and initially put it down to allergies or a sinus infection.

When the problems continued, he was advised against racing.

"Because of my symptoms and my history with concussions, and after my recent wrecks at Michigan and Daytona, I met with a neurological specialist," said Earnhardt.

"After further evaluation, they felt it was best for me to sit out."

Duchardt declined to speculate on how long Earnhardt's absence might continue.

"The most important thing in this process is for Dale to feel better," he said.

"I'm not going to speculate on Dale's future.

"The important thing is Dale recognised he had something going on and took a step out."

Earnhardt has yet to win a race this year but is currently among the provisional Chase field based on his points score.

He will need a waiver from NASCAR to qualify for the Chase now he is missing a race, but the series has already given one to Tony Stewart this season and 2015 champion Kyle Busch benefited from such a dispensation after breaking his leg last year.

Duchardt said Hendrick could wait until Wednesday next week to decide whether Earnhardt or Gordon would race at Indianapolis and has not planned beyond that.

"Speculating past [Indianapolis] is assuming Dale won't be ready for that amount of time," he said.

"We'll be thinking about contingency plans but we don't have anything formalised."

New Hampshire substitute Bowman was a Cup regular with the Tommy Baldwin Racing team last season and has raced part-time for Earnhardt's JR Xfinity squad this year.

"It's definitely not the circumstances that I wanted to get an opportunity like this," said Bowman.

"Obviously I'm hoping Dale feels better but at the same time it's the best opportunity I've ever had in my life."