George Friend bundled the ball home in the seventh minute of stoppage-time to earn a point at The Den, but Pulis says his squad are not strong enough to get promoted.
Middlesbrough were beaten in the play-off semi-finals by Aston Villa last season and are among the favourites to challenge this season. But having lost a number of key players, including centre-back Ben Gibson having signed yesterday for Burnley for £15m, Pulis says the club must buy in order to compete.
He said: “We have to put things in perspective here. If you look at the team we had compared to the team that ended last season, we’re six players down. Ben Gibson, Adama Traore, Roberto Ayala, Patrick Bamford, Muhamed Besic – they’re all top players. So that team [Saturday] was a massive change.
“We know we have to bring players in. That group is not good enough to get us promoted. It’s a smashing group, but it’s not good enough to get us promoted. We need to add to the group.”
Millwall dominated for the majority of the game and led through goals from Aiden O’Brien and Lee Gregory, after an error from Boro debutant Aden Flint, with 87 minutes on the clock.
Pulis added: “The players worked very hard. We were very average in the first half. It was only the last 20, 25 minutes that we started to have a go.”
Millwall: Archer, Romeo, Hutchinson, Cooper, Meredith, Jed Wallace, Williams, Saville, O’Brien (Skalak 86), Gregory (Elliott 81), Morison (Murray Wallace 90). Unused substitutes: McLaughlin, Onyedinma, Amos, Tunnicliffe.
Middlesbrough: Randolph, Shotton, Flint, Fry, Friend, Clayton (Tavernier 59), Leadbitter (Wing 56), Howson, Downing (Fletcher 74), Assombalonga, Braithwaite. Unused substitutes: Konstantopoulos, Johnson, Wood-Gordon, Chapman.
Referee: K Friend (Leicestershire).