Jenson Button expects Stoffel Vandoorne to learn quickly as he makes his F1 debut for McLaren at the Bahrain Grand Prix.
Alonso suffered fractured ribs and lung damage in his crash at the Australian Grand Prix, meaning Vandoorne will take his place this weekend. The Belgian driver won three out of the six Bahrain races he competed in during GP2, including two in his dominant title-winning season last year.
Button admits McLaren will miss Alonso's feedback from the car this weekend but thinks Vandoorne is more than capable of getting to a good level of his own.
"I'm not surprised Fernando is not driving this weekend and that hurts a bit our preparation, but Stoffel won here last year in GP2 so he knows the track and the team well," Button said. "He never drove this car but hopefully he'll learn quickly and we can trust his feedback, because it's very important to keep both cars running.
"We never know how good anyone is until you put him in a Formula One car, so let's wait and see. It's obviously a very late call for Stoffel but this team is very good at preparing its drivers. He obviously knows the circuit very well and he knows the team well too. We're very limited with testing here, as always, so we need as much information as possible from both cars to be ready for qualifying."
Alonso has decided to stay in Bahrain this weekend despite the fact he will watch proceedings from the sidelines, somewhere Button thinks the Spaniard can still be a help to the team.
"I would have done the thing as Fernando if I couldn't race -- I would stay on. You wait around quite a while for the next grand prix and then to be told you're not allowed to race... I'm sure it's going to be an exciting weekend and Fernando would rather be in the car but let's see how it goes. His input will be helpful."