The United coach spoke out as McNamara awaits his fate after appealing to the Scottish Football Association over his five-match ban for a touchline altercation with the St Johnstone manager Tommy Wright during last month's league encounter at Tannadice.
United beat Rangers 3-1 in last weekend's semi-final to book their place against the Perth side in next month's final at Celtic Park. McNamara had appealed against the ban which allowed him to take his place in the Ibrox dugout, but is now in danger of having to watch from the stand after his three-game immediate touchline ban kicked in.
The SFA are yet to announce a date for McNamara's hearing but Jackson made his own position on the matter clear. "It's ridiculous, the manager has got to lead his team out for the Scottish Cup final," insisted the coach. "I think he'll be speaking to the chairman about it. We're hugely disappointed with what he got.
"The boys had a couple of days off and everyone is buzzing from being in the final. We've just got to concentrate on the league between now and the final and that's where the coaching staff come into it. We still believe we can finish second. That's going to take a monster effort but that's what we have to focus on first and foremost before any cup final. That is fact. We're not going to try and gloss over anything. We want to finish as high up as possible."
Jackson insists United will not be be reading too much into this weekend's match with St Johnstone at McDiarmid Park.
"It's the fourth time we'll have played them. We know how the play and they know how we play so it doesn't affect Saturday's game. You would imagine Tommy Wright will be thinking the exact same about Saturday. He'll be wanting his side to finish as high up the league as possible. The cup final is irrelevant just now. It's still five weeks away."
Jackson has been impressed by the job Wright has done at McDiarmid Park and has fond memories of their time together at Newcastle United.
"Tommy bought my house in Morpeth when we were together at Newcastle in 1988. I done him! I'm good friends with Tommy and it's great for him. He has done a great job."
Jackson can understand why the St Johnstone striker Stevie May, whose two goals secured their place in the final, has been attracting so much interest this season, but does not see that as unsettling for the player or the manager.
"It's just part and parcel of football. If nobody was interested in his players, then maybe he wouldn't be doing the right job. They're doing a great job so people are going to watch their players. It's the same here. It's a compliment people being interested in your players, not a hindrance. It's great and I think the boys thrive on it as well."
Jackson featured in the 1991 Scottish Cup final when United were beaten by Motherwell and cannot wait to try to get his hands on the famous old trophy.
"It will be a proud moment for everyone involved with Dundee United. I've only been to one cup final and that was with Dundee United, against Motherwell in 1991. "As a manager and a coach, you appreciate it that wee bit more. It's because you're looking after a whole bunch of boys. You are responsible for them. It doesn't matter where the final is. It should be at Hampden but it can't be and it will be a fantastic occasion."