"It is a big day for Don," says Glenn, "and I suppose he will have to endure booing every time he touches the ball, but that is a backhanded compliment.
"The fans there didn't want him to leave and they shouldn't because he scored 10 goals for them last season."
Glenn says Don is still settling in at Upton Park and adds: "It takes time for all new players to settle in but he has had good games such as at home to Newcastle and away to Ipswich, and he will be looking consistently to show that sort of form."
One player who could have been lining up against the Hammers this weekend is Trevor Sinclair - when he asked for a transfer Sunderland expressed an interest but were not able to meet West Ham's valuation.
That doesn't disappoint Glenn, who says: "There has not been interest from Sunderland for a number of weeks and the less we get the better.
"Trevor is working hard and is very motivated."
The game will give Glenn an opportunity to meet up with Kevin Phillips, whom he brought to Watford from Baldock Town for next to nothing when he was boss at Vicarage Road, and he says: "There hasn't been a Kevin Phillips since and everyone is looking hard enough - he cost £10,000 and is now worth £10m.
"He is a wonderful professional and a good role model for any young player - his goalscoring record since going to Sunderland is phenomenal.
"He didn't score last week and I hope he doesn't score against us but we will have to work hard.
"We know the way Sunderland will play with a lot of balls into the penalty box; it is a useful tactic and has paid dividends in the last few seasons so if we don't win it against Niall Quinn we have to pick up the second ball."
As for last week's action, Glenn says: "It was disappointing to lose in front of our own fans but it was always going to be a particularly difficult game with the four players we had missing.
"We do not have a big enough squad to be able to handle easily the loss of Kanoute, Winterburn, Carrick, and Di Canio - while they had a full strength side, as they have had for the last six weeks.
"The boys battled hard but unfortunately we lost 1-0 and after only picking up one point in three games we need a win at Sunderland.
"Losing the lead at Charlton in injury time was a huge disappointment; we threw away two points that night and at this stage every other point would have helped.
"But the return of David James and Joe Cole has been very much on plus side. It was, of course, David's first game against Spurs and he was unfortunate with the goal and the ball coming off the post for Les Ferdinand.
"Joe was full of energy and he can pick up on that performance in the next few games; there is no doubt he is over his foot injury."