The Hornets have failed to score in the league this season and he has no financial resources to buck the trend.
"It was a disappointing result and a disappointing performance," he said after the 2-0 defeat at the Stadium of Light.
"We were very poor and got what we deserved. We were really poor in the first half and while we showed more spirit in the second half, it was too little too late.
No excuses from Lewington
"We can't score goals and that is worrying. In the previous two matches we had shots saved and kicked off the line, but today it was clear to see how lightweight we are."
SUNDERLAND MATCH REPORT
SUNDERLAND MATCH REPORT