The boss issued the warning ahead of the tricky Boxing Day clash against a Charlton outfit in form and no doubt gunning for revenge after our 1-0 win at the Valley earlier in the season.
Monday's fine 3-2 victory over Manchester City stretched our unbeaten run to five games and lifted us back into seventh place in the Premiership, within points of the European places.
Glenn insisted: "We've put in a good run but in football you want to be greedy and continue it.
"We're at home to Charlton next and after winning here (at City) and playing so well against Arsenal, a game we should have won, this is where football can come and kick you in the teeth.
"We've got to be professional. We enjoy this win for 20 minutes and then start planning for the next one because they come thick and fast at this time of year.
"We've responded after a nasty little run. Every club has had an inconsistent run and it's how you respond.
"I'm pleased we've gone unbeaten for this period of time but Charlton won't be easy.
"They've had 48 hours more rest and they are on an unbeaten run as well.
"I've seen them a couple of times recently and they are good side, an organised side and an under-rated side. It won't be easy for us."
Having missed Monday's win, skipper Teddy Sheringham is unlikely to feature against Charlton after picking up a knee injury in training.
Glenn suggested that Gary Doherty (knee), Les Ferdinand (toe) and Mauricio Taricco (throat infection) all have 'an outside chance' of recovering in time.
Jamie Redknapp (broken toe) and Anthony Gardner (knee) remain out.
Glenn Hoddle has reminded his confident side of football's nasty habit of kicking you in the teeth when things appear to be going well.