Monk returns to Elland Road with new club Boro for the first time on Sunday (1.15pm) since quitting as Leeds manager in May.
Middlesbrough hit form before the international break to climb to fifth in the Championship table while Leeds have lost seven of their last nine games.
Speaking at a pre-match press conference before the game, Christiansen said: “Middlesbrough are a very good team but we know also what their weaknesses are.
“All the teams here will make it difficult for Leeds.”
There was speculation about Christiansen’s future in the wake of the 3-1 defeat at Brentford before the international break.
But Leeds managing director Angus Kinnear publicly backed the 44-year-old, stressing the club are taking a long-term approach to success.
Christiansen said: “I said a bad run would come. We are making a project of several years where almost everyone is new in this, starting from the chairman and the sporting director.
“Our target is still to be in the top six. I would have preferred to have had a game after the defeat but on the other hand you have time to think about things.”
Christiansen admits Leeds’ poor form has “not been so nice” on a personal level, but added: “If you don’t care, that would be a big problem.”
Leeds and Middlesbrough were both tipped for promotion at the start of the season.
Boro currently have the edge but Christiansen has faith his squad can seal all three points.
“We are only three points away from each other and that can soon turn,” he said.
“We are in a bad situation of results but not in the way we play.
“I believe in the players, they are still the best for me.”
Leeds have a fully-fit squad available for Middlesbrough’s trip to Elland Road.
Northern Ireland winger Stuart Dallas has recovered from a “small problem” while summer signing Caleb Ekuban is “ready”.