Both men had MRIs - A.J. Pollock on his elbow, Yasmany Tomas on his knee - and the good news is that neither appeared to show any significant structural damage. However, the players have been benched until at least next Wednesday.
Pollock came into spring training with elbow soreness, and was held out of the early going. He has appeared in three games so far, going 1-for-8. According to manager Chip Hale, Pollock "takes too many tees and flips in the cage and throws too much, and his right arm is getting fatigued. We're going to dial it back and let him build it back up, and try to keep away from any extra use of it." It's clearly very important for the team to have A.J. fit and well for Opening Day, as he was second only to Paul Goldschmidt in his value last year, whether you prefer bWAR or fWAR - and the gap was probably smaller than you expected (less than one win by fWAR).
Yasmany Tomas has been even more limited, managing only a pair of games, and is still looking for his first spring hit, having gone 0-for-5. He did get seven (!) at-bats in a B-game over the weekend, though that may have played a part in his knee condition flaring up. Tomas's roster situation is a little different, having not performed up to hopes in 2015 - however, a leaner, meaner Yasmany showed up in spring, and fans were hoping he would live up to those expectations this year, though he is competing with Socrates Brito for the everyday job in left-field. "We'll let it cool down and take it slow," said Hale. "We're trying to get the swelling out of there."
For both players, caution at this point is likely very wise, and there's no indication so far this won't be cleared up in rime for the regular season. Hale pointed out that the team can easily rack up the at-bats for a player as needed in minor-league contests, in order to get them ready in time. Still, we'll be happier when they've proven themselves 100% healthy again.