The company cancelled the majority of its services between Yorkshire and London on Sunday.
Rail industry insiders said that all 65 of the Hitachi-manufactured Azuma trains are being investigated for potential cracks on their chassises after Great Western Railway, who also operate the model, discovered the defect during routine maintenance.
In a statement, released on Tuesday, an LNER spokesman said: “A temporary, amended timetable will remain in place until Friday May 14, across the LNER route. This is due to a number of Hitachi Class 800 trains from several train companies being taken out of service for ongoing checks as a precautionary measure.
"The issue with the Class 800 trains continues to be investigated. Once trains have been checked, they are being reintroduced back into service as soon as possible.
"In addition, LNER is due to introduce an InterCity 225 train back into service tomorrow ahead of the original reintroduction date planned for June.
"Customers are being asked to check before they travel and ensure they have a seat reservation. We apologise for any disruption caused. The latest information can be found at lner.co.uk.”