Yes, it is a potential worry. He did his fist stint (and, i think, only stint in the game) and came off at the end of that and didn't return. It looked at the time that it was a planned interchange rather than as a result of injury. If memory serves me correctly, he didn't come back. O'Donnell was possibly the interchange with Sidlow and he went on to do a very lengthy stint on debut.
It could be the case that Sidlow is being rested, the game was safe by the time in the second half he might have otherwise have been expected to come back on. It could be that O'Donnell was having such a good run out that Lam felt it was more beneficial to keep him on and Sidlow could then be kept wrapped in cotton wool.
For me, he (Sidlow) is a prize asset particularly given that he was one of only two uninjured props that we had going in to the game.
Dick, you say that he wasn't there on the pitch at the end of the game and I must say that I did not notice that. However, I saw that he was with the replacements for most of the second half and I noticed that he was standing for a good part of that half. If he is injured then perhaps it is no more than a niggle. I certainly hope that, if he is injured, that it is not serious. We need him fit and firing every week until at least either or both Ioane and Green are back. As everyone on this forum knows, we are really short of front rowers at the moment even when (if ever) they are all fit.
Derek, Chester and Lam know the situation. However I, for one, am confident that this shortage is likely to be addressed before the end of the season if and when the right prop comes available. I appreciate that O'Donnell is a second rower but his signing clearly demonstrates that the club, behind the scenes and without press speculation, are constantly scanning the available talent down under and that when the right man becomes available that they are then straight in for him.
For the moment it will be a case of make do and mend, probably with temporary loan signings from Saints or Wigan.
But, going back to your original point, I agree that if Sidlow is injured that it is a worry, in fact a huge worry, in more ways than one.