Salehi's hint at a strenuous stage in the diplomatic talks came while the new round of nuclear negotiations between Iran and the Group 5+1 (Russia, China, the US, Britain, France and Germany) in the Swiss city of Lausanne entered its third day on Saturday.
Iranian Foreign Minister Mohammad Javad Zarif and US Secretary of State John Kerry have held several bilateral meetings over the past days.
Other foreign ministers from the Group 5+1 (also known as the P5+1 or E3+3) are expected to join the Lausanne talks as well.
Salehi said the parties should assess whether they would be able to reach a consensus before the ministers arrive in Lausanne.
On Saturday evening, Zarif is scheduled to meet his French and German counterparts, Laurent Fabius and Frank Walter Steinmeier, in the Swiss city.
Diplomats are working to agree on a preliminary framework accord by the end of March, to be followed by a comprehensive deal by June 30 that includes all technical details.
The long-awaited comprehensive deal aims to end more than a decade of impasse over Tehran's civilian nuclear activities.