CJ van der Linde's return to South Africa and Cian Healey's international commitments means Leinster start the season with the services of just three props - Heinke van der Merwe, Mike Ross and Ronan McCormack
Leinster chief executive Mick Dawson said: "At the minute it doesn't look great and we're planning on the basis that we'll be without Stan until next year.
"It's a serious setback given how good he has been for us and it doesn't help that most of the good props around the place are already under contract.
"Certainly we'll have to go outside Ireland to find a replacement and we've already been in touch with the IRFU on that. We'll try and identify someone as soon as possible and take it from there."