Weather permitting, Marco Andretti will briefly shake down the #29 McLaren-Honda-Andretti entry for the Spanish legend, before Alonso steps in to turn his first laps on the iconic 2.5-mile oval.

Alonso entered six grands prix on the IMS road course, retiring from the first three, sitting out the fourth along with all the Michelin runners in 2005, before finishing fifth and second respectively in the final two Formula 1 races there, in 2006 and '07.

Andretti Autosport team manager Rob Edwards, who flew straight from IndyCar's test at Gateway on Tuesday to complete last-minute preparations for Alonso's test at IMS, told Motorsport.com: "Marco's going to head out at 9am, weather permitting – it's going to be pretty cold overnight – basically shake the car down. IndyCar rules allow him to do just 10 laps.

"Then we put Fernando in and make our way through the day. The intention is to actually try and pass the Rookie Orientation Practice in this test, and then during the ROP and Refreshers period on Monday 15 May, which runs from 12 noon to 2pm, he will be permitted two sets of tires to do the Refresher test.

"Every rookie is allowed one oval test before the practice week for the Indy 500, so that's what we're using in this first test."

Rookie orientation practice can vary year to year, but for this year's 101st running of the Indy 500, it involves 10 laps at 205-210mph, 15 laps at 210-215mph, and 15 laps over 215mph.

"Those speeds will be achievable with the downforce levels still relatively 'comfortable'," said Edwards.

"Obviously the idea is to get Fernando to a comfort level where he's just getting used to constantly driving at those speeds, so it doesn't make sense to get into a big trimming exercise on Day 1.

"That's particularly true if the day's cold. You know, cold weather is a double-edged sword – the dense atmosphere provides more downforce, but it's also difficult to get tyre temperature up to where you want it."

Edwards explained that as well as a shakedown and systems check on the car, Andretti's role would be to establish a baseline set-up for Alonso, as he joins the team that has won four Indianapolis 500s, including two of the last three.

"Obviously we had strong cars at the Speedway last year," he said, "but there have been some changes to the tire we're using at the Speedway this year, so the intention is for Marco to run a setup that we know and check that this setup works in terms of car behavior with the new tyre.

"That will give us a good baseline to establish how our setups are working and how best to proceed with Fernando."

Alonso did not spectate at the Gateway test on Tuesday, but was instead preparing in Indianapolis.

"He was supposed to get into Indy on Monday night, but he had some issues with his flight," said Edwards, "so instead he did another half day on the Honda simulator on Tuesday, and then he went to our raceshop to continue with his seat-fitting."

Edwards said despite being highly sophisticated, the simulator could not be regarded as a true substitute for genuine seat time.

"It can, to a limited extent, simulate crosswinds," he said, "and that's always a major factor at the Speedway.

"The sim is a great tool to establish certain things, but there are many aspects of Fernando's task that can only truly be established on the racetrack, not least, running in traffic. It's pretty much the biggest part of being competitive in the race.

"But Fernando will have the track to himself tomorrow. In the garage, he's going to have a real braintrust of advisors though!

"Gil de Ferran, Michael [Andretti] and Bryan [Herta], Marco, Alex [Rossi, reigning Indy 500 champion] and Jack Harvey [who won the Indy Lights Freedom 100 at IMS and who will make his IndyCar debut in the 500 driving a sixth Andretti Autosport entry].

"So a cast of thousands, right?! And they'll all be useful to Fernando. But in the end there's no substitute for him being out there and learning his own way."

Motorsport.com will be streaming Alonso's test live today.