Spain were off colour as the friendly affair finished goalless in Cluj, a result that followed an similarly underwhelming performance in a 1-1 draw against Italy on Thursday.
The likes of Cesc Fabregas, Juan Mata, Aritz Aduriz and Alvaro Morata all came on in the second half but the pattern of the game never changed, leaving head coach Del Bosque with much to ponder ahead their defence of their European Championships crown this summer.
"I'm not happy at all following two draws from my team," he said.
READ MORE | Toothless Spain held by Romania
"We lacked everything, in all areas. I tried to win the game by making changes, but it did not change anything.
"Romania have played a very good match. They did not let us play our football, they are a good side."
Koke admitted Spain were well below their usual standard, but the Atletico Madrid midfielder is confident they will improve by the time the Euros come around in a little over two months.
"The feeling we have is one of annoyance because we did not win," he said. "But we will improve in the tournament.
"We are a good group and we'll be fine."