He picked up the injury early on during the province's RaboDirect PRO12 win over Edinburgh at the RDS and had to be helped off the pitch.
Strauss' latest injury lay-off will see him miss the knockout stages of the PRO12 and he will play no part in Ireland's June Test against Argentina.
The Leinster squad trained in UCD today ahead of the visit of Ulster to the RDS on Saturday (kick-off 7pm) in the second of the league play-offs.
Fit-again back rower Sean O'Brien came through the Edinburgh game unscathed and has trained well this week, reporting no issues.
Another player back from injury, Fergus McFadden, has also trained well this week and is available for selection again this weekend.
Elsewhere Eoin Reddan continues to make slow but steady progress from his shoulder injury - a final decision on his availability will not be made until later in the week.
Meanwhile, Mike McCarthy's injury is not as bad as first thought. He is unlikely to feature this weekend, and similarly, Luke Fitzgerald will not be available for selection.
Tickets for the Leinster-Ulster clash are still on sale at www.leinsterrugby.ie/tickets, as are tickets for the British & Irish Cup final against Leeds Carnegie at Donnybrook on Friday, May 23.