Sebastian Kehl says Shinji Kagawa would be welcomed back to Borussia Dortmund with open arms.
Douglas has described his arrival at Barcelona as the pinnacle of his career ahead of their visit to Villarreal on Sunday.
Wigan chairman Dave Whelan believes manager Roberto Martinez is destined for the top of European football.
Martinez takes Wigan to Liverpool in the Barclays Premier League this weekend for the first time since rejecting the opportunity to take the reins at Anfield this summer.
Consequently, Brendan Rodgers left Martinez's former employers Swansea to succeed Kenny Dalglish and the Reds lie 13th in the table ahead of the Anfield clash - one point and one place above Latics.
Throughout the negotiation process, where Martinez broke off his close-season holiday to hold talks with Liverpool's owners in Miami, Whelan stated the 38-year-old was destined for the pinnacle of the game and that position has not changed.
He said: "Roberto will be the manager of one of the top three clubs in Europe, I don't think there's any doubt about that."
Whelan was speaking at the North West Football Awards where he was honoured with a lifetime achievement award in recognition of his achievements with Wigan, who he took control of when they were struggling in the fourth tier of English football.
The 75-year-old's close personal relationship with Martinez is seen as a key factor in the Spaniard's decision to remain at the DW Stadium, but Whelan also identified the decision to sign him as a player along with compatriots Jesus Seba and Isidro Diaz after becoming chairman in 1995 as a decisive moment in Wigan's history.
"We have a very, very good working relationship, Roberto and myself," he said. I signed him from Spain and he played for Wigan Athletic with the other two boys - the Three Amigos they were called.
"That changed our future because Wigan Athletic then became a team with people playing from Spain who played football from back to front.
"It changed our style and changed the life of Wigan Athletic when I signed those three boys."
Martinez has stuck diligently to such footballing principles during two improbable escapes from relegation trouble over the past two seasons, winning no shortage of admirers in collecting vital wins over the likes of Manchester United and Arsenal.
Inconsistency continues to dog Wigan - Saturday's defeat to West Brom on the back of victory at Tottenham standing as the latest example - but Whelan has higher sights for the current campaign.
He added: "We have one aim - to finish in the top half of the league.
"We've had aims of staying in the Premier League. This season, we want to finish in the top half. That is what we're going to do."