According to Yahoo! Japan, Endo is shooting for recovering by July’s Natsu Basho. Any later and he would likely be demoted from Makuuchi into Juryo. However, his oyakata does not want to rush things so if he’s not 100% he will not compete.
update* I think Endo will be ranked M12 or M13 in May and he’ll need to go kyujo for the whole tournament. The article says they don’t even know yet if he’ll need surgery. They haven’t assessed because of the swelling. Going kyujo in May will drop him into Juryo already for the July tournament. This is what happened to Homasho last year. He was M2 with one win when he was injured. Next tournament he was M13 and kyujo. Then he was demoted all the way to Juryo 9, going kyujo again dropped to Makushita 7 and announced his retirement. Endo has a bit of an advantage since he had 4 wins when he was injured but he was also ranked lower at M5.