Hearts interim boss Jon Daly criticised Ian Cathro's training methods, claiming the players are not fit enough.
Daly took charge following Cathro's dismissal before the start of the league season, and felt his side were lacking in their 0-0 draw with Rangers.
"(It is) satisfying to come to Ibrox and get a clean sheet," said Daly.
"We need to get the players a little fitter, then we give ourselves a better chance when we come to places like Ibrox."
Daly has taken charge of Hearts' first three Premiership games as he waits to find out if he will get the job on a permanent basis.
After a 4-1 defeat to Celtic on the opening day, he has strengthened his case with four points out of six at Kilmarnock and Rangers.
The Irishman told BBC Scotland: "As a club we probably could have done more with them (in pre-season training), but obviously the manager was trying to implement the 3-4-3 system at the time and make sure he had that covered.
"But from my point of view the fitness levels are off where I would personally like them to be, where we can then work a game extremely hard off the ball and have the fitness levels to then kick on when you have the ball as well.
"I'm trying to get across to the players the effort and work-rate that I require from them, and that takes its toll on the attacking players when we get the ball back."
John Souttar hit the crossbar for Hearts as they held Pedro Caixinha's side to a draw.
Rangers' Alfredo Morelos had a goal disallowed for offside while Bruno Alves' header was cleared off the line, and team-mate Kenny Miller was denied by Hearts goalkeeper Jack Hamilton before the break.
"We had a couple of opportunities," said Daly. "We lacked a bit of composure, but I can't fault the work rate and effort of the players.
"I don't think we did enough to win the game but I don't think we deserved to lose it. We forced them into the areas where we were quite comfortable. I don't remember our goalkeeper Jack Hamilton having a lot to do."