Great Britain lost their fifth game in succession by suffering a 90-80 defeat against Lithuania in Houston, Texas.
GB guard Kyle Johnson came off the bench to score 18 points, shooting four from seven from three-point range.
Forward Pops Mensah-Bonsu - who scored 16-points and put in four big blocks - blamed himself for the GB defeat after shooting 50% from the free-throw line.
Mensah-Bonsu said: "Put this loss squarely on my shoulders. That (50%) is going to kill us and kill me.''
On a brighter note, centre Joel Freeland recovered from a poor first half to add 14 points and seven rebounds. GB's guards made a significant contribution, with veteran Nate Reinking and Kyle Johnson combining for 21 points in the first half.
This was a high-intensity game that GB should have won. Deep in the second quarter, they led by 14 points and had Lithuania in panic mode after going on a 14-0 run.
Playing in just his second game on the camp, Mensah-Bonsu caused Lithuania untold trouble under the basket, drawing foul after foul, but he could not translate that domination into points.
At half-time GB led the Lithuania by seven points. But Lithuania - rattled by their own recent poor form and desperate for a victory before going to the Olympic qualifying tournament next week - came out in the second half quicker and sharper.
Their guard Martynas Pocius found himself in space and knocked down a hat-trick of three-point shots as Lithuania took the lead in the third, for the first time since early in the first period.
Johnson replied with a hat-trick of his own to get GB in front again in what was a highly frenetic period of play in which seven three-point shots were netted in quick succession. But Lithuania won the third period 31-19.
Lithuania's star players, guard Linus Kleiza and centre Jonas Valanciunas, fouled out in the fourth and it was then that GB threatened a comeback.
Mensah-Bonsu's huge block at one end of the court was followed up by a brilliant twisting two-point jumper from Freeland and with just minutes remaining it was a one-point game.
But Lithuania's depth came to the fore as Jonas Maciulis netted his only three-point shot of the game, that pulled them ahead again.
GB return to the UK on Sunday before internationals against France and Spain next weekend.
Although the BBC understand the cuts to the line-up have already been agreed internally, no official announcement will be made before 5 July when the 12 going to the Olympics will be named.