IDIOMS

last thing one needs

(idiomatic) Something not wanted by someone, who is already burdened.

Example: 2011 September 24, David Ornstein, “Arsenal 3 - 0 Bolton”[1], BBC Sport:
  With Yossi Benayoun, Jack Wilshere and Thomas Vermaelen already sidelined, the last thing Arsene Wenger needs is more injuries.