Millwall came from behind to win 2-1 at Middlesbrough yesterday afternoon to move up to second in the Championship table and push Town down to fourth.
The Blues' scheduled Good Friday game at Southampton had to be postponed due to the Saints reaching the FA Cup quarter-finals, meaning they now have two games in hand and a three point gap to make up.
With league leaders Coventry City unlikely to be caught, McKenna was asked whether he felt his side were in a three-way fight for second spot.
"I think, until it's impossible, you'd never rule out teams," replied the Blues boss, whose side host Birmingham City, at Portman Road, on Easter Monday (3pm).
"There's teams below who are probably thinking if they can win six or seven games before the end of the season, then they might be there. I would never discount that.
"The only focus can be on what we can do. We have eight games and we're going to have to win a good proportion of them - whether that's five wins, six wins, seven wins, you don't know.
"You can't control what other teams do, apart from the game we play against Middlesbrough (at Portman Road on Sunday, April 19). The only way to think is to go and try and win your next one."
Town's final eight fixtures come over a hectic 27 day spell.
"We know we're going to have to perform well across a really busy spell," said McKenna.
"It's still pretty tight up there. I'm sure there'll be a few teams that have their eyes on doing something special over the last month. And we're one of them."