"We're a week by week team, so we know we are in for a tough one this week and the last thing we want is a hiccup against the Leopards," said the former All Black flyhalf.
With the Lions at the top of the log, five points clear of Western Province after nine games, and the Leopards languishing in bottom spot, the visitors will look to bag a full five points from the match.
Spencer stressed his side could not afford to take a semi-final qualification for granted and would need to keep improving.
"We're a long way from that. We've got to win another four or five games and that's our main focus," he said.
"We will focus on the Leopards and get it out the way, then we'll move to the Bulls (for next week's clash) come Monday.
"The semi-finals and the finals are a long way away, and we've got a lot of rugby before then."
Despite the newly promoted Leopards struggling in the premier division, Spencer insisted the hosts would present a challenge.
"The boys are still excited. We're sort of, not quite, halfway through the second round.
"It's a tough one away this week against the Leopards in Potch, and they're starting to play some good rugby, so they'll be a difficult side to beat."
After the Leopards game, the Lions face a difficult run-in to the playoffs, with clashes against the Blue Bulls, Free State Cheetahs, Western Province and the Sharks.
"After this week, we have the big four, so it only gets tougher from here," Spencer said.
One of the revelations for the Lions this season has been the performance of flyhalf Elton Janties, and while Spencer applauded the 21-year-old pivot for his efforts, he admitted they were still trying to improve his game.
"His goalkicking has got better as the season has gone on, and his decision making too," he said.
"It's something that can always be improved, though, along with (scrumhalf) Michael Bondesio.
"He's (Jantjies) come back with a bit of a spark this season, and loves taking the ball to the line.
"He loves being a threat, not only on attack, but on defence - he doesn't mind making tackles.
"We're very happy with how he's gone with the Lions this year and what he can do for us in the future."