With his side bottom of the Premier League and seven points from safety, Poyet revealed that he only has 17 fit first-team players to choose from.
"Injuries come through contact and that is football," he said. "But other ones come when there is tension and nerves.
"They all come with tiredness and especially the mental side of things.
"We have gone from having a full squad - with the exception of Westie (Keiren Westwood) for the (League Cup) final last month - to now having seven or eight players missing.
"That's normal. It's nothing against the players, it's the tension, the nerves and the pressure.
"(Steven) Fletcher and Westie are out injured, and Liam (Bridcutt) is out for personal reasons, while Phil (Bardsley) is suspended. But we also have three or four other injuries, and one ill.
"They have all come together so, for the first time in my time here, we cannot make 18 for the game. That's not the best timing!"
Sunderland beat City 1-0 in November's reverse fixture but surrendered a one-goal advantage to lose the League Cup final to Manuel Pellegrini's side in March.
'I don’t think he’s good enough, passing often goes wrong. We are somewhat limited up front but even then, you have to earn your selection, and I think he doesn’t deserve that now.' Manchester United star Joshua Zirkzee slammed by national team manager
'Manchester United look confused about what they're being asked to do - he's certainly not getting the best out of them., I wouldn't bet a single penny on them getting to the next round' Alan Shearer issues damning verdict of Europa League hopes
