Fernando Alonso's Monaco absence this weekend is not "professional", according to Felipe Massa.
Alonso's former Ferrari teammate Massa was asked about the Spaniard's decision to skip F1's prestigious street race to bid for Indy 500 victory.
"It was a surprise," Massa told Spanish daily Marca, "but he's doing it because McLaren has a big, big problem.
"To be honest, I respect his decision but to stop racing in Formula 1 to do another race is not normal. I think it's not 100% professional."
Massa said it is possible that Alonso will leave McLaren-Honda at the end of the season.
"It's very difficult to answer, but if he has the opportunity to go to a competitive team, if McLaren does not give him what he needs, I think he would leave yesterday," said the Brazilian.
A frustrating start to the season has left McLaren pointless at the bottom of the team rankings.