"If you look at the statistics, Bottas is on average closer to Hamilton's times than Rosberg was," said the former Ferrari and Sauber driver.
"But he also knows that he is under pressure. Valtteri needs to win a few races, because he has a contract at Mercedes for only one year," Salo added.
Salo, 50, also commented on the fate of Russian driver Daniil Kvyat, who after a tumultuous 2016 season is now fighting back for F1 credibility this year.
"Daniil had a difficult year last year, with significant issues," said the Finn.
"But I'm glad that he is now back in shape and going better than Sainz. I'm sure Kvyat has a good future in formula one," Salo added.