Millwall relied on a late Ben Thompson equaliser in injury time to avoid a shock FA Cup exit to Rochdale.

The Lions, who featured a rotated starting 11 for the cup tie, took the lead through a Jed Wallace penalty before being pegged back by an Ian Henderson strike on 32 minutes.

Dale took the lead when Matt Done tapped in an equaliser eight minutes after the restart, before Thompson’s late run secured a replay at the Spotland stadium.

Here are five things we learned…

Shackell did well since coming in, but it nearly never happened

The 34-year-old, who has joined the club on loan from Derby County until the end of the season, almost had his debut curtailed through illness.

Neil Harris said in his post-match conference that the defender suffered food poisoning the day before but urged the Millwall boss to start him against Rochdale regardless.

Shackell impressed in his 60-minute cameo, despite his discomfort which was later described as ‘probably the worst he’s ever felt on a football field’.

Tony Craig’s days at Millwall continue to look numbered

The Lions’ defence was not as resolute as many have come to expect against Rochdale, however the centre back had his weaknesses put on display by the opposition.

It’s unnecessary to blame him for Rochdale’s second, after the ball bizarrely looped over goalkeeper David Martin for an easy tap-in, but he was unsettled a lot of the time.

This is now Craig’s fourth spell at the Den but it does not look to be continuing beyond this summer – and could end before the window closes.

Tom Elliott did not have his shooting boots on – literally

Last summer’s signing was seen with some new footwear after half-time when the two sides went in level at 1-1.

He looked to have struggled against the opposition’s back three, getting outmuscled and pushed out of position.

When he did get his chances, they were saved, blocked, or wide of the target. Not the best outing for Elliott.

Rochdale (almost) deserved to win the game

When Fred Onyedinma won the penalty that led to the opening goal by Jed Wallace, it gave Millwall some reprieve.

But even after the goal it was Rochdale who still looked comfortable and made the game as even as possible.

Perhaps they were unlucky to concede so late through midfielder Ben Thompson, but it looked like one of those days they would come away with a win.

FA Cup run or not, Millwall should go as far as they can in it this season

Rochdale, who are in League One’s relegation zone, present a very good opportunity for the Lions to reach the latter stages of this year’s competition.

No one expects them to reach the final at Wembley, à la the 2004 showpiece with Manchester United, but it would be very disappointing if they did not at least get past a ‘weaker’ opposition at this stage.

The team, by Harris’ own admission, was strong enough to win but a replay in Manchester on a weekday night is not the most ideal scenario.