Reading pair Sean Morrison and Jordan Obita have both signed new contracts at the Madejski Stadium.
Ipswich defender Aaron Cresswell has signed a two-year extension to his contract.
SK Lierse have announced the loan signing of Celtic striker Tony Watt.
Lierse, who sit 12th in Belgium's top flight, revealed on their website that the 19-year-old had joined on a season-long deal.
Watt has scored eight goals in 21 appearances for Celtic - including what proved to be the winner against Barcelona in the Champions League - but was being offered to clubs on loan during pre-season.
Watt departed after Celtic completed their second signing in two days by bringing in Finnish forward Teemu Pukki but there was frustration for Neil Lennon in his attempts to further strengthen his squad before Saturday night's Scottish transfer deadline.
Celtic had at least three bids for winger Lee Tomlin rejected, the first believed to be for £1.2million, and attempts to sign Manchester United's Alexander Buttner on loan have failed to bear fruit.
Pukki signed a four-year deal in the morning after completing his move from Schalke as Celtic added to the signing of Israeli midfielder Nir Biton 24 hours earlier.
But their bid to sign Tomlin before the 11pm Saturday night deadline did not go down well in Peterborough.
Posh manager Darren Ferguson substituted the 24-year-old at half-time in their 2-0 defeat by Crawley, which ended the League One side's 100 percent record this season.
Ferguson said, according to the Peterborough Telegraph: "The third bid arrived during the game. If that's how Celtic want to do business that's up to them, but it didn't do Lee any favours.
"The first bid they made was a waste of time anyway. They can't have watched him much over the past few years if that's all they think it's worth.
"He's not going anywhere anyway and he knows that. We have great experience of clubs bidding for our players and they never leave after one bid."
Ferguson, who is hoping to complete a deal for Livingston's Scotland Under-21 midfielder Stefan Scougall, added: "Lee is a lad who loves playing football and I did think that when he got on to the pitch he would forget about the Celtic bids, but clearly that wasn't the case."
Chairman Darragh MacAnthony added on Twitter: "I used to be a Celtic fan. Not after today! What a day."
Lennon earlier revealed Tomlin and Buttner were among several options.
Lennon said: "Buttner is a player who came to our attention in the last day or so. I have seen him play in midfield or on the left side, or off the striker.
"I would like him to play further forward through the middle. He is a really intelligent footballer with a big build, a very good footballer."
There was little transfer activity elsewhere with the vast majority of Scottish Premiership clubs having completed their transfer business before the final day, although Kilmarnock manager Allan Johnston hopes to bring in two free agents in the coming weeks.
St Johnstone manager Tommy Wright had been hoping to sign a Barclays Premier League player on loan but admitted Scotland's earlier deadline might scupper his plans.
The only other confirmed activity involving Scottish Premiership clubs saw three young players going on loan. Arbroath signed Hibernian defender Brad Donaldson and Motherwell striker Lee Erwin, while St Johnstone defender Gareth Rodger joined Montrose.