Rubens Barrichello agrees with Sebastian Vettel that Kimi Raikkonen might struggle to re-adapt to formula one.
World champion Vettel said this week he can imagine "it would be very difficult to return straight away to the same level as before" after a two-year absence from F1.
Brazilian Barrichello, who was an outside contender for the Lotus Renault race seat now occupied by the 2007 world champion and Finn, agrees.
"We only have the example of Schumacher," said the 39-year-old, referring to Michael Schumacher who struggled last year when he returned to F1 after a three-year retirement.
"If there was someone who we could be sure would walk back in and be there (on the pace), it was him.
"They (Raikkonen and Schumacher) are different so you can't say whether it will be easier or harder (for Raikkonen)," Barrichello is quoted by Brazil's Globo.
"But I have no doubt that after two years off, he will feel the difference in terms of how the category has changed, and of course the tyres."
F1 chief executive Bernie Ecclestone said Raikkonen's return is good news.
"I am really happy to see Kimi again where he belongs, in formula one," the 81-year-old is quoted by German news agency DPA.