The visitors failed to make their numerical advantage pay as 10-man Doncaster ran out 2-1 winners at the Keepmoat Stadium to secure their first victory in five games.
Dean Furman's early goal had put the home side ahead, before Byron Webster equalised against his former club on the stroke of half-time.
Furman was then sent off for a second booking, but Mark Duffy's first goal for Rovers was enough to leave Yeovil rooted to the foot of the table.
And Johnson revealed that attracting players to Yeovil had proved difficult following their promotion in the summer, with several targets not keen on relocating to Somerset.
"It's disappointing because we billed it as a very important game to win but we didn't really get our game going," said Johnson.
"We didn't show enough quality to win a Championship game on the day.
"When you go 11 v 10 you've got to keep the ball and we weren't able to do that. I think some of the boys froze on the day in the build-up to what was a very important game.
"I've got a bit of work to do between now and January.
"I've given everyone that came up from the first division with us an opportunity to play in the Championship and some have taken it well and some haven't.
"We need to get these reinforcements now if we can to build a Championship squad.
"It's not easy for us to get people because we're not a big city - Yeovil's not on the sat-nav.
"We've chased quite a few players and we'll keep chasing and every now and then one will stick."
Doncaster bossed the early possession, and deserved their breakthrough after 11 minutes.
Mark Duffy intercepted a loose Frazer Fyvie pass on halfway and progressed to the edge of the penalty box, before feeding Federico Macheda in down the left channel - the striker's square ball leaving Furman a simple finish from six yards.
The visitors improved but there had been little sign of an equaliser when a Joe Ralls free-kick in the 43rd minute picked out Shane Duffy, and the centre-half's downward header across the six-yard box was fired home by Webster.
Midfielder Furman picked up a second yellow card for a clumsy challenge on Ed Upson with 10 minutes remaining, but just two minutes later Joel Edwards clumsily bundled Mark Duffy over on the edge of the box and the 28-year-old picked himself up to curl the subsequent free-kick in at the near post.
"It was a fantastic result but a scrappy performance from us" said Rovers boss Paul Dickov, whose side move five points clear of the relegation zone.
"When we got the goal I thought 'we can go on and get a couple here', but we seemed to lose the tempo of the game a little bit and the two banks of four dropped too deep. You can't switch on and off in games.
"The players have got to get a lot of credit because going down to 10 men at 1-1 the tendency is to sit back and take the point.
"I asked them what was wrong at half-time. It looked as if we weren't enjoying passing the ball so I asked them to up it."